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SDL源代码分析系列文章上市：
SDL2源码分析5：更新纹理（SDL_UpdateTexture()）
SDL2源码分析6：拷贝到渲染器（SDL_RenderCopy()）
SDL2源码分析7：显示（SDL_RenderPresent()）
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上一篇文章分析了SDL中创建窗体的函数SDL_CreateWindow()。这篇文章继续分析SDL的源码。
本文分析SDL的渲染器（SDL_Renderer）。
SDL播放视频的代码流程例如以下所看到的。
初始化:SDL_Init(): 初始化SDL。循环渲染数据:
SDL_CreateWindow(): 创建窗体（Window）。
SDL_CreateRenderer(): 基于窗体创建渲染器（Render）。
SDL_CreateTexture(): 创建纹理（Texture）。
SDL_UpdateTexture(): 设置纹理的数据。
SDL_RenderCopy(): 纹理复制给渲染器。SDL_RenderPresent(): 显示。
上篇文章分析了该流程中的第2个函数SDL_CreateWindow()。
本文继续分析该流程中的第3个函数SDL_CreateRenderer()。
SDL_Renderer
SDL_Renderer结构体定义了一个SDL2中的渲染器。假设直接使用SDL2编译好的SDK的话。是看不到它的内部结构的。
有关它的定义在头文件里仅仅有一行代码。例如以下所看到的。
/** * rief A structure representing rendering state */ struct SDL_Renderer; typedef struct SDL_Renderer SDL_Renderer;
在源码project中能够看到SDL_Renderer的定义，位于renderSDL_sysrender.h文件里。
它的定义例如以下。
/* Define the SDL renderer structure */
struct SDL_Renderer
{
const void *magic;
void (*WindowEvent) (SDL_Renderer * renderer, const SDL_WindowEvent *event);
int (*GetOutputSize) (SDL_Renderer * renderer, int *w, int *h);
int (*CreateTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
int (*SetTextureColorMod) (SDL_Renderer * renderer,
SDL_Texture * texture);
int (*SetTextureAlphaMod) (SDL_Renderer * renderer,
SDL_Texture * texture);
int (*SetTextureBlendMode) (SDL_Renderer * renderer,
SDL_Texture * texture);
int (*UpdateTexture) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * rect, const void *pixels,
int pitch);
int (*UpdateTextureYUV) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * rect,
const Uint8 *Yplane, int Ypitch,
const Uint8 *Uplane, int Upitch,
const Uint8 *Vplane, int Vpitch);
int (*LockTexture) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * rect, void **pixels, int *pitch);
void (*UnlockTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
int (*SetRenderTarget) (SDL_Renderer * renderer, SDL_Texture * texture);
int (*UpdateViewport) (SDL_Renderer * renderer);
int (*UpdateClipRect) (SDL_Renderer * renderer);
int (*RenderClear) (SDL_Renderer * renderer);
int (*RenderDrawPoints) (SDL_Renderer * renderer, const SDL_FPoint * points,
int count);
int (*RenderDrawLines) (SDL_Renderer * renderer, const SDL_FPoint * points,
int count);
int (*RenderFillRects) (SDL_Renderer * renderer, const SDL_FRect * rects,
int count);
int (*RenderCopy) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * srcrect, const SDL_FRect * dstrect);
int (*RenderCopyEx) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * srcquad, const SDL_FRect * dstrect,
const double angle, const SDL_FPoint *center, const SDL_RendererFlip flip);
int (*RenderReadPixels) (SDL_Renderer * renderer, const SDL_Rect * rect,
Uint32 format, void * pixels, int pitch);
void (*RenderPresent) (SDL_Renderer * renderer);
void (*DestroyTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
void (*DestroyRenderer) (SDL_Renderer * renderer);
int (*GL_BindTexture) (SDL_Renderer * renderer, SDL_Texture *texture, float *texw, float *texh);
int (*GL_UnbindTexture) (SDL_Renderer * renderer, SDL_Texture *texture);
/* The current renderer info */
SDL_RendererInfo info;
/* The window associated with the renderer */
SDL_Window *window;
SDL_bool hidden;
/* The logical resolution for rendering */
int logical_w;
int logical_h;
int logical_w_backup;
int logical_h_backup;
/* The drawable area within the window */
SDL_Rect viewport;
SDL_Rect viewport_backup;
/* The clip rectangle within the window */
SDL_Rect clip_rect;
SDL_Rect clip_rect_backup;
/* The render output coordinate scale */
SDL_FPoint scale;
SDL_FPoint scale_backup;
/* The list of textures */
SDL_Texture *textures;
SDL_Texture *target;
Uint8 r, g, b, a; /**< Color for drawing operations values */
SDL_BlendMode blendMode; /**< The drawing blend mode */
void *driverdata;
};通过代码能够看出当中包括了一个“渲染器”应该包括的各种属性。
这个结构体中的各个变量还没有深入研究，暂不具体分析。
以下来看看怎样创建这个SDL_Renderer。
SDL_CreateRenderer()
函数简单介绍
SDL中使用SDL_CreateRenderer()基于窗体创建渲染器。SDL_CreateRenderer()原型例如以下。SDL_Renderer * SDLCALL SDL_CreateRenderer(SDL_Window * window,
int index, Uint32 flags);參数含义例如以下。
window ： 渲染的目标窗体。
index ：打算初始化的渲染设备的索引。
设置“-1”则初始化默认的渲染设备。
flags ：支持以下值（位于SDL_RendererFlags定义中）
SDL_RENDERER_SOFTWARE ：使用软件渲染SDL_RENDERER_ACCELERATED ：使用硬件加速
SDL_RENDERER_PRESENTVSYNC：和显示器的刷新率同步SDL_RENDERER_TARGETTEXTURE ：不太懂
返回创建完毕的渲染器的ID。假设创建失败则返回NULL。
函数调用关系图
SDL_CreateRenderer()关键函数的调用关系能够用下图表示。
上述图片不太清晰，相冊里面上传了一份原始的大图片：
http://my.csdn.net/leixiaohua1020/album/detail/1793385
源码分析
SDL_CreateRenderer()的源码位于renderSDL_render.c中，例如以下所看到的。
SDL_Renderer * SDL_CreateRenderer(SDL_Window * window, int index, Uint32 flags)
{
#if !SDL_RENDER_DISABLED
SDL_Renderer *renderer = NULL;
int n = SDL_GetNumRenderDrivers();
const char *hint;
if (!window) {
SDL_SetError("Invalid window");
return NULL;
}
if (SDL_GetRenderer(window)) {
SDL_SetError("Renderer already associated with window");
return NULL;
}
hint = SDL_GetHint(SDL_HINT_RENDER_VSYNC);
if (hint) {
if (*hint == '0') {
flags &= ~SDL_RENDERER_PRESENTVSYNC;
} else {
flags |= SDL_RENDERER_PRESENTVSYNC;
}
}
if (index < 0) {
hint = SDL_GetHint(SDL_HINT_RENDER_DRIVER);
if (hint) {
for (index = 0; index < n; ++index) {
const SDL_RenderDriver *driver = render_drivers[index];
if (SDL_strcasecmp(hint, driver->info.name) == 0) {
/* Create a new renderer instance */
renderer = driver->CreateRenderer(window, flags);
break;
}
}
}
if (!renderer) {
for (index = 0; index < n; ++index) {
const SDL_RenderDriver *driver = render_drivers[index];
if ((driver->info.flags & flags) == flags) {
/* Create a new renderer instance */
renderer = driver->CreateRenderer(window, flags);
if (renderer) {
/* Yay, we got one! */
break;
}
}
}
}
if (index == n) {
SDL_SetError("Couldn't find matching render driver");
return NULL;
}
} else {
if (index >= SDL_GetNumRenderDrivers()) {
SDL_SetError("index must be -1 or in the range of 0 - %d",
SDL_GetNumRenderDrivers() - 1);
return NULL;
}
/* Create a new renderer instance */
renderer = render_drivers[index]->CreateRenderer(window, flags);
}
if (renderer) {
renderer->magic = &renderer_magic;
renderer->window = window;
renderer->scale.x = 1.0f;
renderer->scale.y = 1.0f;
if (SDL_GetWindowFlags(window) & (SDL_WINDOW_HIDDEN|SDL_WINDOW_MINIMIZED)) {
renderer->hidden = SDL_TRUE;
} else {
renderer->hidden = SDL_FALSE;
}
SDL_SetWindowData(window, SDL_WINDOWRENDERDATA, renderer);
SDL_RenderSetViewport(renderer, NULL);
SDL_AddEventWatch(SDL_RendererEventWatch, renderer);
SDL_LogInfo(SDL_LOG_CATEGORY_RENDER,
"Created renderer: %s", renderer->info.name);
}
return renderer;
#else
SDL_SetError("SDL not built with rendering support");
return NULL;
#endif
}SDL_CreateRenderer()中最重要的一个函数就是它调用了SDL_RenderDriver的CreateRenderer()方法。通过该方法能够创建一个渲染器。
环绕着这种方法，包括了一些初始化工作以及一些收尾工作。
以下针对这个最核心的函数进行分析。
我们首先来看一下SDL_RenderDriver这个结构体。从字面的意思能够看出它代表了“渲染器的驱动程序”。
这个结构体的定义例如以下。
/* Define the SDL render driver structure */
struct SDL_RenderDriver
{
SDL_Renderer *(*CreateRenderer) (SDL_Window * window, Uint32 flags);
/* Info about the renderer capabilities */
SDL_RendererInfo info;
};从代码中能够看出，这个结构体的成员比較简单。包括了一个函数指针CreateRenderer()和一个存储信息的SDL_RendererInfo类型的结构体info。CreateRenderer()是用于创建渲染器的函数，而SDL_RendererInfo则包括了该结构体的一些信息。能够看一下SDL_RendererInfo的定义。
/**
* rief Information on the capabilities of a render driver or context.
*/
typedef struct SDL_RendererInfo
{
const char *name; /**< The name of the renderer */
Uint32 flags; /**< Supported ::SDL_RendererFlags */
Uint32 num_texture_formats; /**< The number of available texture formats */
Uint32 texture_formats[16]; /**< The available texture formats */
int max_texture_width; /**< The maximimum texture width */
int max_texture_height; /**< The maximimum texture height */
} SDL_RendererInfo;在SDL中有一个全局的SDL_RenderDriver类型的静态数组render_drivers，当中存储了SDL支持的全部渲染器。
该数组定义例如以下。
static const SDL_RenderDriver *render_drivers[] = {
#if SDL_VIDEO_RENDER_D3D
&D3D_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_D3D11
&D3D11_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_OGL
&GL_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_OGL_ES2
&GLES2_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_OGL_ES
&GLES_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_DIRECTFB
&DirectFB_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_PSP
&PSP_RenderDriver,
#endif
&SW_RenderDriver
};从render_drivers数组的定义能够看出，当中包括了Direct3D，OpenGL。OpenGL ES等各种渲染器的驱动程序。
我们能够选择几个看一下。
比如Direct3D的渲染器驱动程序D3D_RenderDriver的定义例如以下（位于renderdirect3dSDL_render_d3d.c）。
SDL_RenderDriver D3D_RenderDriver = {
D3D_CreateRenderer,
{
"direct3d",
(SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
1,
{SDL_PIXELFORMAT_ARGB8888},
0,
0}
};能够看出创建Direct3D渲染器的函数是D3D_CreateRenderer()。
OpenGL的渲染器驱动程序GL_RenderDriver的定义例如以下（位于renderopenglSDL_render_gl.c）。
SDL_RenderDriver GL_RenderDriver = {
GL_CreateRenderer,
{
"opengl",
(SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
1,
{SDL_PIXELFORMAT_ARGB8888},
0,
0}
};能够看出创建OpenGL渲染器的函数是GL_CreateRenderer()。
软件渲染器驱动程序SW_RenderDriver的定义例如以下（位于rendersoftwareSDL_render_sw.c）。
SDL_RenderDriver SW_RenderDriver = {
SW_CreateRenderer,
{
"software",
SDL_RENDERER_SOFTWARE | SDL_RENDERER_TARGETTEXTURE,
8,
{
SDL_PIXELFORMAT_RGB555,
SDL_PIXELFORMAT_RGB565,
SDL_PIXELFORMAT_RGB888,
SDL_PIXELFORMAT_BGR888,
SDL_PIXELFORMAT_ARGB8888,
SDL_PIXELFORMAT_RGBA8888,
SDL_PIXELFORMAT_ABGR8888,
SDL_PIXELFORMAT_BGRA8888
},
0,
0}
};能够看出创建软件渲染器的函数是SW_CreateRenderer ()。
有关SDL_RenderDriver这个结构体就不再多说了。以下分别看一下Direct3D，OpenGL，Software这三种最常见的渲染器的创建方法。
1. Direct3D
Direct3D 的渲染器在创建函数是D3D_CreateRenderer()。该函数位于renderdirect3dSDL_render_d3d.c文件里。首先看一下它的代码。
SDL_Renderer * D3D_CreateRenderer(SDL_Window * window, Uint32 flags)
{
SDL_Renderer *renderer;
D3D_RenderData *data;
SDL_SysWMinfo windowinfo;
HRESULT result;
const char *hint;
D3DPRESENT_PARAMETERS pparams;
IDirect3DSwapChain9 *chain;
D3DCAPS9 caps;
DWORD device_flags;
Uint32 window_flags;
int w, h;
SDL_DisplayMode fullscreen_mode;
int displayIndex;
renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
if (!renderer) {
SDL_OutOfMemory();
return NULL;
}
data = (D3D_RenderData *) SDL_calloc(1, sizeof(*data));
if (!data) {
SDL_free(renderer);
SDL_OutOfMemory();
return NULL;
}
if (!D3D_LoadDLL(&data->d3dDLL, &data->d3d)) {
SDL_free(renderer);
SDL_free(data);
SDL_SetError("Unable to create Direct3D interface");
return NULL;
}
renderer->WindowEvent = D3D_WindowEvent;
renderer->CreateTexture = D3D_CreateTexture;
renderer->UpdateTexture = D3D_UpdateTexture;
renderer->UpdateTextureYUV = D3D_UpdateTextureYUV;
renderer->LockTexture = D3D_LockTexture;
renderer->UnlockTexture = D3D_UnlockTexture;
renderer->SetRenderTarget = D3D_SetRenderTarget;
renderer->UpdateViewport = D3D_UpdateViewport;
renderer->UpdateClipRect = D3D_UpdateClipRect;
renderer->RenderClear = D3D_RenderClear;
renderer->RenderDrawPoints = D3D_RenderDrawPoints;
renderer->RenderDrawLines = D3D_RenderDrawLines;
renderer->RenderFillRects = D3D_RenderFillRects;
renderer->RenderCopy = D3D_RenderCopy;
renderer->RenderCopyEx = D3D_RenderCopyEx;
renderer->RenderReadPixels = D3D_RenderReadPixels;
renderer->RenderPresent = D3D_RenderPresent;
renderer->DestroyTexture = D3D_DestroyTexture;
renderer->DestroyRenderer = D3D_DestroyRenderer;
renderer->info = D3D_RenderDriver.info;
renderer->info.flags = (SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);
renderer->driverdata = data;
SDL_VERSION(&windowinfo.version);
SDL_GetWindowWMInfo(window, &windowinfo);
window_flags = SDL_GetWindowFlags(window);
SDL_GetWindowSize(window, &w, &h);
SDL_GetWindowDisplayMode(window, &fullscreen_mode);
SDL_zero(pparams);
pparams.hDeviceWindow = windowinfo.info.win.window;
pparams.BackBufferWidth = w;
pparams.BackBufferHeight = h;
if (window_flags & SDL_WINDOW_FULLSCREEN) {
pparams.BackBufferFormat =
PixelFormatToD3DFMT(fullscreen_mode.format);
} else {
pparams.BackBufferFormat = D3DFMT_UNKNOWN;
}
pparams.BackBufferCount = 1;
pparams.SwapEffect = D3DSWAPEFFECT_DISCARD;
if (window_flags & SDL_WINDOW_FULLSCREEN) {
if ((window_flags & SDL_WINDOW_FULLSCREEN_DESKTOP) == SDL_WINDOW_FULLSCREEN_DESKTOP) {
pparams.Windowed = TRUE;
pparams.FullScreen_RefreshRateInHz = 0;
} else {
pparams.Windowed = FALSE;
pparams.FullScreen_RefreshRateInHz = fullscreen_mode.refresh_rate;
}
} else {
pparams.Windowed = TRUE;
pparams.FullScreen_RefreshRateInHz = 0;
}
if (flags & SDL_RENDERER_PRESENTVSYNC) {
pparams.PresentationInterval = D3DPRESENT_INTERVAL_ONE;
} else {
pparams.PresentationInterval = D3DPRESENT_INTERVAL_IMMEDIATE;
}
/* Get the adapter for the display that the window is on */
displayIndex = SDL_GetWindowDisplayIndex(window);
data->adapter = SDL_Direct3D9GetAdapterIndex(displayIndex);
IDirect3D9_GetDeviceCaps(data->d3d, data->adapter, D3DDEVTYPE_HAL, &caps);
device_flags = D3DCREATE_FPU_PRESERVE;
if (caps.DevCaps & D3DDEVCAPS_HWTRANSFORMANDLIGHT) {
device_flags |= D3DCREATE_HARDWARE_VERTEXPROCESSING;
} else {
device_flags |= D3DCREATE_SOFTWARE_VERTEXPROCESSING;
}
hint = SDL_GetHint(SDL_HINT_RENDER_DIRECT3D_THREADSAFE);
if (hint && SDL_atoi(hint)) {
device_flags |= D3DCREATE_MULTITHREADED;
}
result = IDirect3D9_CreateDevice(data->d3d, data->adapter,
D3DDEVTYPE_HAL,
pparams.hDeviceWindow,
device_flags,
&pparams, &data->device);
if (FAILED(result)) {
D3D_DestroyRenderer(renderer);
D3D_SetError("CreateDevice()", result);
return NULL;
}
/* Get presentation parameters to fill info */
result = IDirect3DDevice9_GetSwapChain(data->device, 0, &chain);
if (FAILED(result)) {
D3D_DestroyRenderer(renderer);
D3D_SetError("GetSwapChain()", result);
return NULL;
}
result = IDirect3DSwapChain9_GetPresentParameters(chain, &pparams);
if (FAILED(result)) {
IDirect3DSwapChain9_Release(chain);
D3D_DestroyRenderer(renderer);
D3D_SetError("GetPresentParameters()", result);
return NULL;
}
IDirect3DSwapChain9_Release(chain);
if (pparams.PresentationInterval == D3DPRESENT_INTERVAL_ONE) {
renderer->info.flags |= SDL_RENDERER_PRESENTVSYNC;
}
data->pparams = pparams;
IDirect3DDevice9_GetDeviceCaps(data->device, &caps);
renderer->info.max_texture_width = caps.MaxTextureWidth;
renderer->info.max_texture_height = caps.MaxTextureHeight;
if (caps.NumSimultaneousRTs >= 2) {
renderer->info.flags |= SDL_RENDERER_TARGETTEXTURE;
}
if (caps.PrimitiveMiscCaps & D3DPMISCCAPS_SEPARATEALPHABLEND) {
data->enableSeparateAlphaBlend = SDL_TRUE;
}
/* Store the default render target */
IDirect3DDevice9_GetRenderTarget(data->device, 0, &data->defaultRenderTarget );
data->currentRenderTarget = NULL;
/* Set up parameters for rendering */
D3D_InitRenderState(data);
if (caps.MaxSimultaneousTextures >= 3)
{
#ifdef ASSEMBLE_SHADER
/* This shader was created by running the following HLSL through the fxc compiler
and then tuning the generated assembly.
fxc /T fx_4_0 /O3 /Gfa /Fc yuv.fxc yuv.fx
--- yuv.fx ---
Texture2D g_txY;
Texture2D g_txU;
Texture2D g_txV;
SamplerState samLinear
{
Filter = ANISOTROPIC;
AddressU = Clamp;
AddressV = Clamp;
MaxAnisotropy = 1;
};
struct VS_OUTPUT
{
float2 TextureUV : TEXCOORD0;
};
struct PS_OUTPUT
{
float4 RGBAColor : SV_Target;
};
PS_OUTPUT YUV420( VS_OUTPUT In )
{
const float3 offset = {-0.0625, -0.5, -0.5};
const float3 Rcoeff = {1.164, 0.000, 1.596};
const float3 Gcoeff = {1.164, -0.391, -0.813};
const float3 Bcoeff = {1.164, 2.018, 0.000};
PS_OUTPUT Output;
float2 TextureUV = In.TextureUV;
float3 yuv;
yuv.x = g_txY.Sample( samLinear, TextureUV ).r;
yuv.y = g_txU.Sample( samLinear, TextureUV ).r;
yuv.z = g_txV.Sample( samLinear, TextureUV ).r;
yuv += offset;
Output.RGBAColor.r = dot(yuv, Rcoeff);
Output.RGBAColor.g = dot(yuv, Gcoeff);
Output.RGBAColor.b = dot(yuv, Bcoeff);
Output.RGBAColor.a = 1.0f;
return Output;
}
technique10 RenderYUV420
{
pass P0
{
SetPixelShader( CompileShader( ps_4_0_level_9_0, YUV420() ) );
}
}
*/
const char *shader_text =
"ps_2_0
"
"def c0, -0.0625, -0.5, -0.5, 1
"
"def c1, 1.16400003, 0, 1.59599996, 0
"
"def c2, 1.16400003, -0.391000003, -0.813000023, 0
"
"def c3, 1.16400003, 2.01799989, 0, 0
"
"dcl t0.xy
"
"dcl v0.xyzw
"
"dcl_2d s0
"
"dcl_2d s1
"
"dcl_2d s2
"
"texld r0, t0, s0
"
"texld r1, t0, s1
"
"texld r2, t0, s2
"
"mov r0.y, r1.x
"
"mov r0.z, r2.x
"
"add r0.xyz, r0, c0
"
"dp3 r1.x, r0, c1
"
"dp3 r1.y, r0, c2
"
"dp2add r1.z, r0, c3, c3.z
" /* Logically this is "dp3 r1.z, r0, c3" but the optimizer did its magic */
"mov r1.w, c0.w
"
"mul r0, r1, v0
" /* Not in the HLSL, multiply by vertex color */
"mov oC0, r0
"
;
LPD3DXBUFFER pCode;
LPD3DXBUFFER pErrorMsgs;
LPDWORD shader_data = NULL;
DWORD shader_size = 0;
result = D3DXAssembleShader(shader_text, SDL_strlen(shader_text), NULL, NULL, 0, &pCode, &pErrorMsgs);
if (!FAILED(result)) {
shader_data = (DWORD*)pCode->lpVtbl->GetBufferPointer(pCode);
shader_size = pCode->lpVtbl->GetBufferSize(pCode);
PrintShaderData(shader_data, shader_size);
} else {
const char *error = (const char *)pErrorMsgs->lpVtbl->GetBufferPointer(pErrorMsgs);
SDL_SetError("Couldn't assemble shader: %s", error);
}
#else
const DWORD shader_data[] = {
0xffff0200, 0x05000051, 0xa00f0000, 0xbd800000, 0xbf000000, 0xbf000000,
0x3f800000, 0x05000051, 0xa00f0001, 0x3f94fdf4, 0x00000000, 0x3fcc49ba,
0x00000000, 0x05000051, 0xa00f0002, 0x3f94fdf4, 0xbec83127, 0xbf5020c5,
0x00000000, 0x05000051, 0xa00f0003, 0x3f94fdf4, 0x400126e9, 0x00000000,
0x00000000, 0x0200001f, 0x80000000, 0xb0030000, 0x0200001f, 0x80000000,
0x900f0000, 0x0200001f, 0x90000000, 0xa00f0800, 0x0200001f, 0x90000000,
0xa00f0801, 0x0200001f, 0x90000000, 0xa00f0802, 0x03000042, 0x800f0000,
0xb0e40000, 0xa0e40800, 0x03000042, 0x800f0001, 0xb0e40000, 0xa0e40801,
0x03000042, 0x800f0002, 0xb0e40000, 0xa0e40802, 0x02000001, 0x80020000,
0x80000001, 0x02000001, 0x80040000, 0x80000002, 0x03000002, 0x80070000,
0x80e40000, 0xa0e40000, 0x03000008, 0x80010001, 0x80e40000, 0xa0e40001,
0x03000008, 0x80020001, 0x80e40000, 0xa0e40002, 0x0400005a, 0x80040001,
0x80e40000, 0xa0e40003, 0xa0aa0003, 0x02000001, 0x80080001, 0xa0ff0000,
0x03000005, 0x800f0000, 0x80e40001, 0x90e40000, 0x02000001, 0x800f0800,
0x80e40000, 0x0000ffff
};
#endif
if (shader_data != NULL) {
result = IDirect3DDevice9_CreatePixelShader(data->device, shader_data, &data->ps_yuv);
if (!FAILED(result)) {
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_YV12;
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_IYUV;
} else {
D3D_SetError("CreatePixelShader()", result);
}
}
}
return renderer;
}D3D_CreateRenderer()这个函数的代码非常长。在这里提取它最重点的几个进行简单的分析。
PS：因为这个函数中包括了大量的Direct3D的API。这方面假设不熟悉的话。能够參考以下两篇文章：
《最简单的视音频播放演示样例3：Direct3D播放YUV，RGB（通过Surface）》
《最简单的视音频播放演示样例4：Direct3D播放RGB（通过Texture）》
（1） 为SDL_Renderer分配内存这一步比較简单。直接使用SDL_calloc()分配内存就能够了。
SDL_calloc()实际上就是calloc()。这一点在前面的文章中已经叙述，在这里不再反复。
（2） 载入Direct3D
载入Direct3D通过函数D3D_LoadDLL()完毕。
调用该函数能够得到一个IDirect3D9类型的接口。IDirect3D9接口能够用于完毕D3D兴许的初始化工作。
D3D_LoadDLL()函数的代码例如以下。
SDL_bool D3D_LoadDLL( void **pD3DDLL, IDirect3D9 **pDirect3D9Interface )
{
*pD3DDLL = SDL_LoadObject("D3D9.DLL");
if (*pD3DDLL) {
IDirect3D9 *(WINAPI * D3DCreate) (UINT SDKVersion);
D3DCreate =
(IDirect3D9 * (WINAPI *) (UINT)) SDL_LoadFunction(*pD3DDLL,
"Direct3DCreate9");
if (D3DCreate) {
*pDirect3D9Interface = D3DCreate(D3D_SDK_VERSION);
}
if (!*pDirect3D9Interface) {
SDL_UnloadObject(*pD3DDLL);
*pD3DDLL = NULL;
return SDL_FALSE;
}
return SDL_TRUE;
} else {
*pDirect3D9Interface = NULL;
return SDL_FALSE;
}
}从代码中能够看出，该函数载入了一个“D3D9.DLL”的Dll。而且调用了当中的Direct3DCreate9()方法。
（3） 渲染器接口函数赋值
SDL_Render结构体中有一系列的函数指针，包括了有关渲染器的各种功能。SDL通过调用这些函数指针就能够调用渲染器相应的功能。这是SDL支持多种渲染器的一个重要特点。代码例如以下所看到的。
renderer->WindowEvent = D3D_WindowEvent;
renderer->CreateTexture = D3D_CreateTexture;
renderer->UpdateTexture = D3D_UpdateTexture;
renderer->UpdateTextureYUV = D3D_UpdateTextureYUV;
renderer->LockTexture = D3D_LockTexture;
renderer->UnlockTexture = D3D_UnlockTexture;
renderer->SetRenderTarget = D3D_SetRenderTarget;
renderer->UpdateViewport = D3D_UpdateViewport;
renderer->UpdateClipRect = D3D_UpdateClipRect;
renderer->RenderClear = D3D_RenderClear;
renderer->RenderDrawPoints = D3D_RenderDrawPoints;
renderer->RenderDrawLines = D3D_RenderDrawLines;
renderer->RenderFillRects = D3D_RenderFillRects;
renderer->RenderCopy = D3D_RenderCopy;
renderer->RenderCopyEx = D3D_RenderCopyEx;
renderer->RenderReadPixels = D3D_RenderReadPixels;
renderer->RenderPresent = D3D_RenderPresent;
renderer->DestroyTexture = D3D_DestroyTexture;
renderer->DestroyRenderer = D3D_DestroyRenderer;（4） 创建Device
创建Direct3D的Device通过IDirect3D9_CreateDevice()函数来实现。这一方面的知识不再叙述，能够參考Direct3D创建Device的相关的文章。
（5） 设置渲染状态
设置渲染状态在函数D3D_InitRenderState()中完毕。该部分的知识也不再详述，能够參考Direct3D相关的渲染教程。贴出D3D_InitRenderState()的代码。static void D3D_InitRenderState(D3D_RenderData *data)
{
D3DMATRIX matrix;
IDirect3DDevice9 *device = data->device;
IDirect3DDevice9_SetVertexShader(device, NULL);
IDirect3DDevice9_SetFVF(device, D3DFVF_XYZ | D3DFVF_DIFFUSE | D3DFVF_TEX1);
IDirect3DDevice9_SetRenderState(device, D3DRS_ZENABLE, D3DZB_FALSE);
IDirect3DDevice9_SetRenderState(device, D3DRS_CULLMODE, D3DCULL_NONE);
IDirect3DDevice9_SetRenderState(device, D3DRS_LIGHTING, FALSE);
/* Enable color modulation by diffuse color */
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_COLOROP,
D3DTOP_MODULATE);
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_COLORARG1,
D3DTA_TEXTURE);
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_COLORARG2,
D3DTA_DIFFUSE);
/* Enable alpha modulation by diffuse alpha */
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_ALPHAOP,
D3DTOP_MODULATE);
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_ALPHAARG1,
D3DTA_TEXTURE);
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_ALPHAARG2,
D3DTA_DIFFUSE);
/* Enable separate alpha blend function, if possible */
if (data->enableSeparateAlphaBlend) {
IDirect3DDevice9_SetRenderState(device, D3DRS_SEPARATEALPHABLENDENABLE, TRUE);
}
/* Disable second texture stage, since we're done */
IDirect3DDevice9_SetTextureStageState(device, 1, D3DTSS_COLOROP,
D3DTOP_DISABLE);
IDirect3DDevice9_SetTextureStageState(device, 1, D3DTSS_ALPHAOP,
D3DTOP_DISABLE);
/* Set an identity world and view matrix */
matrix.m[0][0] = 1.0f;
matrix.m[0][1] = 0.0f;
matrix.m[0][2] = 0.0f;
matrix.m[0][3] = 0.0f;
matrix.m[1][0] = 0.0f;
matrix.m[1][1] = 1.0f;
matrix.m[1][2] = 0.0f;
matrix.m[1][3] = 0.0f;
matrix.m[2][0] = 0.0f;
matrix.m[2][1] = 0.0f;
matrix.m[2][2] = 1.0f;
matrix.m[2][3] = 0.0f;
matrix.m[3][0] = 0.0f;
matrix.m[3][1] = 0.0f;
matrix.m[3][2] = 0.0f;
matrix.m[3][3] = 1.0f;
IDirect3DDevice9_SetTransform(device, D3DTS_WORLD, &matrix);
IDirect3DDevice9_SetTransform(device, D3DTS_VIEW, &matrix);
/* Reset our current scale mode */
SDL_memset(data->scaleMode, 0xFF, sizeof(data->scaleMode));
/* Start the render with beginScene */
data->beginScene = SDL_TRUE;
}（6） 创建Shader
创建Shader通过函数IDirect3DDevice9_CreatePixelShader()完毕。
完毕以上步骤之后，Direct3D的渲染器就创建完毕了。
2. OpenGL
OpenGL 的渲染器在创建函数是GL_CreateRenderer()。该函数位于renderopenglSDL_render_gl.c文件里。首先看一下它的代码。
PS：当中用到了OpenGL的非常多API。假设对OpenGL的API还不熟悉的话，能够參考文章：
《最简单的视音频播放演示样例6：OpenGL播放YUV420P（通过Texture，使用Shader）》
SDL_Renderer * GL_CreateRenderer(SDL_Window * window, Uint32 flags)
{
SDL_Renderer *renderer;
GL_RenderData *data;
const char *hint;
GLint value;
Uint32 window_flags;
int profile_mask, major, minor;
SDL_GL_GetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, &profile_mask);
SDL_GL_GetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, &major);
SDL_GL_GetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, &minor);
window_flags = SDL_GetWindowFlags(window);
if (!(window_flags & SDL_WINDOW_OPENGL) ||
profile_mask == SDL_GL_CONTEXT_PROFILE_ES || major != RENDERER_CONTEXT_MAJOR || minor != RENDERER_CONTEXT_MINOR) {
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, 0);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, RENDERER_CONTEXT_MAJOR);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, RENDERER_CONTEXT_MINOR);
if (SDL_RecreateWindow(window, window_flags | SDL_WINDOW_OPENGL) < 0) {
/* Uh oh, better try to put it back... */
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, profile_mask);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, major);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, minor);
SDL_RecreateWindow(window, window_flags);
return NULL;
}
}
renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
if (!renderer) {
SDL_OutOfMemory();
return NULL;
}
data = (GL_RenderData *) SDL_calloc(1, sizeof(*data));
if (!data) {
GL_DestroyRenderer(renderer);
SDL_OutOfMemory();
return NULL;
}
renderer->WindowEvent = GL_WindowEvent;
renderer->GetOutputSize = GL_GetOutputSize;
renderer->CreateTexture = GL_CreateTexture;
renderer->UpdateTexture = GL_UpdateTexture;
renderer->UpdateTextureYUV = GL_UpdateTextureYUV;
renderer->LockTexture = GL_LockTexture;
renderer->UnlockTexture = GL_UnlockTexture;
renderer->SetRenderTarget = GL_SetRenderTarget;
renderer->UpdateViewport = GL_UpdateViewport;
renderer->UpdateClipRect = GL_UpdateClipRect;
renderer->RenderClear = GL_RenderClear;
renderer->RenderDrawPoints = GL_RenderDrawPoints;
renderer->RenderDrawLines = GL_RenderDrawLines;
renderer->RenderFillRects = GL_RenderFillRects;
renderer->RenderCopy = GL_RenderCopy;
renderer->RenderCopyEx = GL_RenderCopyEx;
renderer->RenderReadPixels = GL_RenderReadPixels;
renderer->RenderPresent = GL_RenderPresent;
renderer->DestroyTexture = GL_DestroyTexture;
renderer->DestroyRenderer = GL_DestroyRenderer;
renderer->GL_BindTexture = GL_BindTexture;
renderer->GL_UnbindTexture = GL_UnbindTexture;
renderer->info = GL_RenderDriver.info;
renderer->info.flags = (SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);
renderer->driverdata = data;
renderer->window = window;
data->context = SDL_GL_CreateContext(window);
if (!data->context) {
GL_DestroyRenderer(renderer);
return NULL;
}
if (SDL_GL_MakeCurrent(window, data->context) < 0) {
GL_DestroyRenderer(renderer);
return NULL;
}
if (GL_LoadFunctions(data) < 0) {
GL_DestroyRenderer(renderer);
return NULL;
}
#ifdef __MACOSX__
/* Enable multi-threaded rendering */
/* Disabled until Ryan finishes his VBO/PBO code...
CGLEnable(CGLGetCurrentContext(), kCGLCEMPEngine);
*/
#endif
if (flags & SDL_RENDERER_PRESENTVSYNC) {
SDL_GL_SetSwapInterval(1);
} else {
SDL_GL_SetSwapInterval(0);
}
if (SDL_GL_GetSwapInterval() > 0) {
renderer->info.flags |= SDL_RENDERER_PRESENTVSYNC;
}
/* Check for debug output support */
if (SDL_GL_GetAttribute(SDL_GL_CONTEXT_FLAGS, &value) == 0 &&
(value & SDL_GL_CONTEXT_DEBUG_FLAG)) {
data->debug_enabled = SDL_TRUE;
}
if (data->debug_enabled && SDL_GL_ExtensionSupported("GL_ARB_debug_output")) {
PFNGLDEBUGMESSAGECALLBACKARBPROC glDebugMessageCallbackARBFunc = (PFNGLDEBUGMESSAGECALLBACKARBPROC) SDL_GL_GetProcAddress("glDebugMessageCallbackARB");
data->GL_ARB_debug_output_supported = SDL_TRUE;
data->glGetPointerv(GL_DEBUG_CALLBACK_FUNCTION_ARB, (GLvoid **)&data->next_error_callback);
data->glGetPointerv(GL_DEBUG_CALLBACK_USER_PARAM_ARB, &data->next_error_userparam);
glDebugMessageCallbackARBFunc(GL_HandleDebugMessage, renderer);
/* Make sure our callback is called when errors actually happen */
data->glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB);
}
if (SDL_GL_ExtensionSupported("GL_ARB_texture_rectangle")
|| SDL_GL_ExtensionSupported("GL_EXT_texture_rectangle")) {
data->GL_ARB_texture_rectangle_supported = SDL_TRUE;
data->glGetIntegerv(GL_MAX_RECTANGLE_TEXTURE_SIZE_ARB, &value);
renderer->info.max_texture_width = value;
renderer->info.max_texture_height = value;
} else {
data->glGetIntegerv(GL_MAX_TEXTURE_SIZE, &value);
renderer->info.max_texture_width = value;
renderer->info.max_texture_height = value;
}
/* Check for multitexture support */
if (SDL_GL_ExtensionSupported("GL_ARB_multitexture")) {
data->glActiveTextureARB = (PFNGLACTIVETEXTUREARBPROC) SDL_GL_GetProcAddress("glActiveTextureARB");
if (data->glActiveTextureARB) {
data->GL_ARB_multitexture_supported = SDL_TRUE;
data->glGetIntegerv(GL_MAX_TEXTURE_UNITS_ARB, &data->num_texture_units);
}
}
/* Check for shader support */
hint = SDL_GetHint(SDL_HINT_RENDER_OPENGL_SHADERS);
if (!hint || *hint != '0') {
data->shaders = GL_CreateShaderContext();
}
SDL_LogInfo(SDL_LOG_CATEGORY_RENDER, "OpenGL shaders: %s",
data->shaders ? "ENABLED" : "DISABLED");
/* We support YV12 textures using 3 textures and a shader */
if (data->shaders && data->num_texture_units >= 3) {
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_YV12;
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_IYUV;
}
#ifdef __MACOSX__
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_UYVY;
#endif
if (SDL_GL_ExtensionSupported("GL_EXT_framebuffer_object")) {
data->GL_EXT_framebuffer_object_supported = SDL_TRUE;
data->glGenFramebuffersEXT = (PFNGLGENFRAMEBUFFERSEXTPROC)
SDL_GL_GetProcAddress("glGenFramebuffersEXT");
data->glDeleteFramebuffersEXT = (PFNGLDELETEFRAMEBUFFERSEXTPROC)
SDL_GL_GetProcAddress("glDeleteFramebuffersEXT");
data->glFramebufferTexture2DEXT = (PFNGLFRAMEBUFFERTEXTURE2DEXTPROC)
SDL_GL_GetProcAddress("glFramebufferTexture2DEXT");
data->glBindFramebufferEXT = (PFNGLBINDFRAMEBUFFEREXTPROC)
SDL_GL_GetProcAddress("glBindFramebufferEXT");
data->glCheckFramebufferStatusEXT = (PFNGLCHECKFRAMEBUFFERSTATUSEXTPROC)
SDL_GL_GetProcAddress("glCheckFramebufferStatusEXT");
renderer->info.flags |= SDL_RENDERER_TARGETTEXTURE;
}
data->framebuffers = NULL;
/* Set up parameters for rendering */
GL_ResetState(renderer);
return renderer;
}GL_CreateRenderer()这个函数的代码非常长。
在这里提取它最重点的几个进行简单的分析。
（1） 为SDL_Renderer分配内存
这一步比較简单。
直接使用SDL_calloc()分配内存就能够了。
（2） 渲染器接口函数赋值
SDL_Render结构体中有一系列的函数指针，包括了有关渲染器的各种功能。这一点在Direct3D的时候已经提过。不再反复。代码例如以下。
renderer->WindowEvent = GL_WindowEvent;
renderer->GetOutputSize = GL_GetOutputSize;
renderer->CreateTexture = GL_CreateTexture;
renderer->UpdateTexture = GL_UpdateTexture;
renderer->UpdateTextureYUV = GL_UpdateTextureYUV;
renderer->LockTexture = GL_LockTexture;
renderer->UnlockTexture = GL_UnlockTexture;
renderer->SetRenderTarget = GL_SetRenderTarget;
renderer->UpdateViewport = GL_UpdateViewport;
renderer->UpdateClipRect = GL_UpdateClipRect;
renderer->RenderClear = GL_RenderClear;
renderer->RenderDrawPoints = GL_RenderDrawPoints;
renderer->RenderDrawLines = GL_RenderDrawLines;
renderer->RenderFillRects = GL_RenderFillRects;
renderer->RenderCopy = GL_RenderCopy;
renderer->RenderCopyEx = GL_RenderCopyEx;
renderer->RenderReadPixels = GL_RenderReadPixels;
renderer->RenderPresent = GL_RenderPresent;
renderer->DestroyTexture = GL_DestroyTexture;
renderer->DestroyRenderer = GL_DestroyRenderer;
renderer->GL_BindTexture = GL_BindTexture;
renderer->GL_UnbindTexture = GL_UnbindTexture;（3） 初始化OpenGL
初始化OpenGL各种变量，包括SDL_GL_CreateContext()，SDL_GL_MakeCurrent()，GL_LoadFunctions()等函数。这一部分还没有具体分析。
（4） 初始化Shader
对Shader的初始化在函数GL_CreateShaderContext()中完毕。
GL_CreateShaderContext()的代码例如以下（位于renderopenglSDL_shaders_gl.c）。
GL_ShaderContext * GL_CreateShaderContext()
{
GL_ShaderContext *ctx;
SDL_bool shaders_supported;
int i;
ctx = (GL_ShaderContext *)SDL_calloc(1, sizeof(*ctx));
if (!ctx) {
return NULL;
}
if (SDL_GL_ExtensionSupported("GL_ARB_texture_rectangle")
|| SDL_GL_ExtensionSupported("GL_EXT_texture_rectangle")) {
ctx->GL_ARB_texture_rectangle_supported = SDL_TRUE;
}
/* Check for shader support */
shaders_supported = SDL_FALSE;
if (SDL_GL_ExtensionSupported("GL_ARB_shader_objects") &&
SDL_GL_ExtensionSupported("GL_ARB_shading_language_100") &&
SDL_GL_ExtensionSupported("GL_ARB_vertex_shader") &&
SDL_GL_ExtensionSupported("GL_ARB_fragment_shader")) {
ctx->glGetError = (GLenum (*)(void)) SDL_GL_GetProcAddress("glGetError");
ctx->glAttachObjectARB = (PFNGLATTACHOBJECTARBPROC) SDL_GL_GetProcAddress("glAttachObjectARB");
ctx->glCompileShaderARB = (PFNGLCOMPILESHADERARBPROC) SDL_GL_GetProcAddress("glCompileShaderARB");
ctx->glCreateProgramObjectARB = (PFNGLCREATEPROGRAMOBJECTARBPROC) SDL_GL_GetProcAddress("glCreateProgramObjectARB");
ctx->glCreateShaderObjectARB = (PFNGLCREATESHADEROBJECTARBPROC) SDL_GL_GetProcAddress("glCreateShaderObjectARB");
ctx->glDeleteObjectARB = (PFNGLDELETEOBJECTARBPROC) SDL_GL_GetProcAddress("glDeleteObjectARB");
ctx->glGetInfoLogARB = (PFNGLGETINFOLOGARBPROC) SDL_GL_GetProcAddress("glGetInfoLogARB");
ctx->glGetObjectParameterivARB = (PFNGLGETOBJECTPARAMETERIVARBPROC) SDL_GL_GetProcAddress("glGetObjectParameterivARB");
ctx->glGetUniformLocationARB = (PFNGLGETUNIFORMLOCATIONARBPROC) SDL_GL_GetProcAddress("glGetUniformLocationARB");
ctx->glLinkProgramARB = (PFNGLLINKPROGRAMARBPROC) SDL_GL_GetProcAddress("glLinkProgramARB");
ctx->glShaderSourceARB = (PFNGLSHADERSOURCEARBPROC) SDL_GL_GetProcAddress("glShaderSourceARB");
ctx->glUniform1iARB = (PFNGLUNIFORM1IARBPROC) SDL_GL_GetProcAddress("glUniform1iARB");
ctx->glUniform1fARB = (PFNGLUNIFORM1FARBPROC) SDL_GL_GetProcAddress("glUniform1fARB");
ctx->glUseProgramObjectARB = (PFNGLUSEPROGRAMOBJECTARBPROC) SDL_GL_GetProcAddress("glUseProgramObjectARB");
if (ctx->glGetError &&
ctx->glAttachObjectARB &&
ctx->glCompileShaderARB &&
ctx->glCreateProgramObjectARB &&
ctx->glCreateShaderObjectARB &&
ctx->glDeleteObjectARB &&
ctx->glGetInfoLogARB &&
ctx->glGetObjectParameterivARB &&
ctx->glGetUniformLocationARB &&
ctx->glLinkProgramARB &&
ctx->glShaderSourceARB &&
ctx->glUniform1iARB &&
ctx->glUniform1fARB &&
ctx->glUseProgramObjectARB) {
shaders_supported = SDL_TRUE;
}
}
if (!shaders_supported) {
SDL_free(ctx);
return NULL;
}
/* Compile all the shaders */
for (i = 0; i < NUM_SHADERS; ++i) {
if (!CompileShaderProgram(ctx, i, &ctx->shaders[i])) {
GL_DestroyShaderContext(ctx);
return NULL;
}
}
/* We're done! */
return ctx;
}上述代码主要完毕了以下两步：
第一步，初始化GL_ShaderContext。GL_ShaderContext中包括了OpenGL的Shader方面用到的各种接口函数。GL_ShaderContext定义例如以下。
struct GL_ShaderContext
{
GLenum (*glGetError)(void);
PFNGLATTACHOBJECTARBPROC glAttachObjectARB;
PFNGLCOMPILESHADERARBPROC glCompileShaderARB;
PFNGLCREATEPROGRAMOBJECTARBPROC glCreateProgramObjectARB;
PFNGLCREATESHADEROBJECTARBPROC glCreateShaderObjectARB;
PFNGLDELETEOBJECTARBPROC glDeleteObjectARB;
PFNGLGETINFOLOGARBPROC glGetInfoLogARB;
PFNGLGETOBJECTPARAMETERIVARBPROC glGetObjectParameterivARB;
PFNGLGETUNIFORMLOCATIONARBPROC glGetUniformLocationARB;
PFNGLLINKPROGRAMARBPROC glLinkProgramARB;
PFNGLSHADERSOURCEARBPROC glShaderSourceARB;
PFNGLUNIFORM1IARBPROC glUniform1iARB;
PFNGLUNIFORM1FARBPROC glUniform1fARB;
PFNGLUSEPROGRAMOBJECTARBPROC glUseProgramObjectARB;
SDL_bool GL_ARB_texture_rectangle_supported;
GL_ShaderData shaders[NUM_SHADERS];
};看这个结构体的定义会给人一种非常混乱的感觉。
不用去理会那些大串的大写字母，仅仅要知道这个结构体是函数的接口的“合集”就能够了。
从函数的名称中我们能够看出有编译Shader的glCreateShaderObject()，glShaderSource()，glCompileShader()等；以及编译Program的glCreateProgramObject()。glAttachObject ()，glLinkProgram()，glUseProgramObject ()等等。
GL_CreateShaderContext()函数中创建了一个GL_ShaderContext并对当中的接口函数进行了赋值。
第二步，编译Shader程序。该功能在CompileShaderProgram()函数中完毕。
CompileShaderProgram()的函数代码例如以下所看到的。
static SDL_bool CompileShaderProgram(GL_ShaderContext *ctx, int index, GL_ShaderData *data)
{
const int num_tmus_bound = 4;
const char *vert_defines = "";
const char *frag_defines = "";
int i;
GLint location;
if (index == SHADER_NONE) {
return SDL_TRUE;
}
ctx->glGetError();
/* Make sure we use the correct sampler type for our texture type */
if (ctx->GL_ARB_texture_rectangle_supported) {
frag_defines =
"#define sampler2D sampler2DRect
"
"#define texture2D texture2DRect
";
}
/* Create one program object to rule them all */
data->program = ctx->glCreateProgramObjectARB();
/* Create the vertex shader */
data->vert_shader = ctx->glCreateShaderObjectARB(GL_VERTEX_SHADER_ARB);
if (!CompileShader(ctx, data->vert_shader, vert_defines, shader_source[index][0])) {
return SDL_FALSE;
}
/* Create the fragment shader */
data->frag_shader = ctx->glCreateShaderObjectARB(GL_FRAGMENT_SHADER_ARB);
if (!CompileShader(ctx, data->frag_shader, frag_defines, shader_source[index][1])) {
return SDL_FALSE;
}
/* ... and in the darkness bind them */
ctx->glAttachObjectARB(data->program, data->vert_shader);
ctx->glAttachObjectARB(data->program, data->frag_shader);
ctx->glLinkProgramARB(data->program);
/* Set up some uniform variables */
ctx->glUseProgramObjectARB(data->program);
for (i = 0; i < num_tmus_bound; ++i) {
char tex_name[10];
SDL_snprintf(tex_name, SDL_arraysize(tex_name), "tex%d", i);
location = ctx->glGetUniformLocationARB(data->program, tex_name);
if (location >= 0) {
ctx->glUniform1iARB(location, i);
}
}
ctx->glUseProgramObjectARB(0);
return (ctx->glGetError() == GL_NO_ERROR);
}从代码中能够看出。这个函数调用了GL_ShaderContext中用于初始化Shader以及Program的各个函数。有关初始化的流程不再细说，能够參考相关的文章。
在该函数中，调用了CompileShader()专门用于初始化Shader。该函数被调用了两次，分别用于初始化vertex shader和fragment shader。
CompileShader()的代码例如以下。
static SDL_bool CompileShader(GL_ShaderContext *ctx, GLhandleARB shader, const char *defines, const char *source)
{
GLint status;
const char *sources[2];
sources[0] = defines;
sources[1] = source;
ctx->glShaderSourceARB(shader, SDL_arraysize(sources), sources, NULL);
ctx->glCompileShaderARB(shader);
ctx->glGetObjectParameterivARB(shader, GL_OBJECT_COMPILE_STATUS_ARB, &status);
if (status == 0) {
GLint length;
char *info;
ctx->glGetObjectParameterivARB(shader, GL_OBJECT_INFO_LOG_LENGTH_ARB, &length);
info = SDL_stack_alloc(char, length+1);
ctx->glGetInfoLogARB(shader, length, NULL, info);
SDL_LogError(SDL_LOG_CATEGORY_RENDER,
"Failed to compile shader:
%s%s
%s", defines, source, info);
#ifdef DEBUG_SHADERS
fprintf(stderr,
"Failed to compile shader:
%s%s
%s", defines, source, info);
#endif
SDL_stack_free(info);
return SDL_FALSE;
} else {
return SDL_TRUE;
}
}从代码中能够看出，该函数调用glShaderSource()。glCompileShader()。glGetObjectParameteriv()这几个函数初始化一个Shader。
Shader的代码位于一个名称为shader_source的char型二维数组里。源码例如以下所看到的。
数组中每一个元素代表一个Shader的代码，每一个Shader的代码包括两个部分：vertex shader代码（相应元素[0]）以及fragment shader代码（相应元素[1]）。
/*
* NOTE: Always use sampler2D, etc here. We'll #define them to the
* texture_rectangle versions if we choose to use that extension.
*/
static const char *shader_source[NUM_SHADERS][2] =
{
/* SHADER_NONE */
{ NULL, NULL },
/* SHADER_SOLID */
{
/* vertex shader */
"varying vec4 v_color;
"
"
"
"void main()
"
"{
"
" gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
"
" v_color = gl_Color;
"
"}",
/* fragment shader */
"varying vec4 v_color;
"
"
"
"void main()
"
"{
"
" gl_FragColor = v_color;
"
"}"
},
/* SHADER_RGB */
{
/* vertex shader */
"varying vec4 v_color;
"
"varying vec2 v_texCoord;
"
"
"
"void main()
"
"{
"
" gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
"
" v_color = gl_Color;
"
" v_texCoord = vec2(gl_MultiTexCoord0);
"
"}",
/* fragment shader */
"varying vec4 v_color;
"
"varying vec2 v_texCoord;
"
"uniform sampler2D tex0;
"
"
"
"void main()
"
"{
"
" gl_FragColor = texture2D(tex0, v_texCoord) * v_color;
"
"}"
},
/* SHADER_YV12 */
{
/* vertex shader */
"varying vec4 v_color;
"
"varying vec2 v_texCoord;
"
"
"
"void main()
"
"{
"
" gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
"
" v_color = gl_Color;
"
" v_texCoord = vec2(gl_MultiTexCoord0);
"
"}",
/* fragment shader */
"varying vec4 v_color;
"
"varying vec2 v_texCoord;
"
"uniform sampler2D tex0; // Y
"
"uniform sampler2D tex1; // U
"
"uniform sampler2D tex2; // V
"
"
"
"// YUV offset
"
"const vec3 offset = vec3(-0.0625, -0.5, -0.5);
"
"
"
"// RGB coefficients
"
"const vec3 Rcoeff = vec3(1.164, 0.000, 1.596);
"
"const vec3 Gcoeff = vec3(1.164, -0.391, -0.813);
"
"const vec3 Bcoeff = vec3(1.164, 2.018, 0.000);
"
"
"
"void main()
"
"{
"
" vec2 tcoord;
"
" vec3 yuv, rgb;
"
"
"
" // Get the Y value
"
" tcoord = v_texCoord;
"
" yuv.x = texture2D(tex0, tcoord).r;
"
"
"
" // Get the U and V values
"
" tcoord *= 0.5;
"
" yuv.y = texture2D(tex1, tcoord).r;
"
" yuv.z = texture2D(tex2, tcoord).r;
"
"
"
" // Do the color transform
"
" yuv += offset;
"
" rgb.r = dot(yuv, Rcoeff);
"
" rgb.g = dot(yuv, Gcoeff);
"
" rgb.b = dot(yuv, Bcoeff);
"
"
"
" // That was easy. :)
"
" gl_FragColor = vec4(rgb, 1.0) * v_color;
"
"}"
},
};有关OpenGL的渲染器的初始化代码临时分析到这里。
3. Software
Software的渲染器在创建函数是SW_CreateRenderer()。该函数位于rendersoftwareSDL_render_sw.c文件里。首先看一下它的代码。
SDL_Renderer * SW_CreateRenderer(SDL_Window * window, Uint32 flags)
{
SDL_Surface *surface;
surface = SDL_GetWindowSurface(window);
if (!surface) {
return NULL;
}
return SW_CreateRendererForSurface(surface);
}从代码中能够看出，SW_CreateRenderer()调用了2个函数：SDL_GetWindowSurface()和SW_CreateRendererForSurface()。SDL_GetWindowSurface()用于创建一个Surface；SW_CreateRendererForSurface()基于Surface创建一个Renderer。
以下分别看一下这2个函数的代码。
SDL_GetWindowSurface()的代码例如以下所看到的（位于videoSDL_video.c）。
SDL_Surface * SDL_GetWindowSurface(SDL_Window * window)
{
CHECK_WINDOW_MAGIC(window, NULL);
if (!window->surface_valid) {
if (window->surface) {
window->surface->flags &= ~SDL_DONTFREE;
SDL_FreeSurface(window->surface);
}
window->surface = SDL_CreateWindowFramebuffer(window);
if (window->surface) {
window->surface_valid = SDL_TRUE;
window->surface->flags |= SDL_DONTFREE;
}
}
return window->surface;
}当中调用了一个函数SDL_CreateWindowFramebuffer()。看一下该函数的代码。
static SDL_Surface * SDL_CreateWindowFramebuffer(SDL_Window * window)
{
Uint32 format;
void *pixels;
int pitch;
int bpp;
Uint32 Rmask, Gmask, Bmask, Amask;
if (!_this->CreateWindowFramebuffer || !_this->UpdateWindowFramebuffer) {
return NULL;
}
if (_this->CreateWindowFramebuffer(_this, window, &format, &pixels, &pitch) < 0) {
return NULL;
}
if (!SDL_PixelFormatEnumToMasks(format, &bpp, &Rmask, &Gmask, &Bmask, &Amask)) {
return NULL;
}
return SDL_CreateRGBSurfaceFrom(pixels, window->w, window->h, bpp, pitch, Rmask, Gmask, Bmask, Amask);
}该函数中调用了SDL_VideoDevice中的一个函数CreateWindowFramebuffer()。
我们以“Windows视频驱动”为例，看看CreateWindowFramebuffer()中的代码。在“Windows视频驱动”下，CreateWindowFramebuffer()相应的函数是WIN_CreateWindowFramebuffer()。
以下看一下该函数的代码。
int WIN_CreateWindowFramebuffer(_THIS, SDL_Window * window, Uint32 * format, void ** pixels, int *pitch)
{
SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
size_t size;
LPBITMAPINFO info;
HBITMAP hbm;
/* Free the old framebuffer surface */
if (data->mdc) {
DeleteDC(data->mdc);
}
if (data->hbm) {
DeleteObject(data->hbm);
}
/* Find out the format of the screen */
size = sizeof(BITMAPINFOHEADER) + 256 * sizeof (RGBQUAD);
info = (LPBITMAPINFO)SDL_stack_alloc(Uint8, size);
SDL_memset(info, 0, size);
info->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
/* The second call to GetDIBits() fills in the bitfields */
hbm = CreateCompatibleBitmap(data->hdc, 1, 1);
GetDIBits(data->hdc, hbm, 0, 0, NULL, info, DIB_RGB_COLORS);
GetDIBits(data->hdc, hbm, 0, 0, NULL, info, DIB_RGB_COLORS);
DeleteObject(hbm);
*format = SDL_PIXELFORMAT_UNKNOWN;
if (info->bmiHeader.biCompression == BI_BITFIELDS) {
int bpp;
Uint32 *masks;
bpp = info->bmiHeader.biPlanes * info->bmiHeader.biBitCount;
masks = (Uint32*)((Uint8*)info + info->bmiHeader.biSize);
*format = SDL_MasksToPixelFormatEnum(bpp, masks[0], masks[1], masks[2], 0);
}
if (*format == SDL_PIXELFORMAT_UNKNOWN)
{
/* We'll use RGB format for now */
*format = SDL_PIXELFORMAT_RGB888;
/* Create a new one */
SDL_memset(info, 0, size);
info->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
info->bmiHeader.biPlanes = 1;
info->bmiHeader.biBitCount = 32;
info->bmiHeader.biCompression = BI_RGB;
}
/* Fill in the size information */
*pitch = (((window->w * SDL_BYTESPERPIXEL(*format)) + 3) & ~3);
info->bmiHeader.biWidth = window->w;
info->bmiHeader.biHeight = -window->h; /* negative for topdown bitmap */
info->bmiHeader.biSizeImage = window->h * (*pitch);
data->mdc = CreateCompatibleDC(data->hdc);
data->hbm = CreateDIBSection(data->hdc, info, DIB_RGB_COLORS, pixels, NULL, 0);
SDL_stack_free(info);
if (!data->hbm) {
return WIN_SetError("Unable to create DIB");
}
SelectObject(data->mdc, data->hbm);
return 0;
}从代码中能够看出，该函数调用了Win32的API函数CreateCompatibleBitmap()，CreateCompatibleDC()等一系列方法创建了“Surface”。
SDL_GetWindowSurface()函数到此分析完毕，如今回过头来再看SW_CreateRenderer ()的还有一个函数SW_CreateRendererForSurface()。
该函数的代码例如以下。
SDL_Renderer * SW_CreateRendererForSurface(SDL_Surface * surface)
{
SDL_Renderer *renderer;
SW_RenderData *data;
if (!surface) {
SDL_SetError("Can't create renderer for NULL surface");
return NULL;
}
renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
if (!renderer) {
SDL_OutOfMemory();
return NULL;
}
data = (SW_RenderData *) SDL_calloc(1, sizeof(*data));
if (!data) {
SW_DestroyRenderer(renderer);
SDL_OutOfMemory();
return NULL;
}
data->surface = surface;
renderer->WindowEvent = SW_WindowEvent;
renderer->GetOutputSize = SW_GetOutputSize;
renderer->CreateTexture = SW_CreateTexture;
renderer->SetTextureColorMod = SW_SetTextureColorMod;
renderer->SetTextureAlphaMod = SW_SetTextureAlphaMod;
renderer->SetTextureBlendMode = SW_SetTextureBlendMode;
renderer->UpdateTexture = SW_UpdateTexture;
renderer->LockTexture = SW_LockTexture;
renderer->UnlockTexture = SW_UnlockTexture;
renderer->SetRenderTarget = SW_SetRenderTarget;
renderer->UpdateViewport = SW_UpdateViewport;
renderer->UpdateClipRect = SW_UpdateClipRect;
renderer->RenderClear = SW_RenderClear;
renderer->RenderDrawPoints = SW_RenderDrawPoints;
renderer->RenderDrawLines = SW_RenderDrawLines;
renderer->RenderFillRects = SW_RenderFillRects;
renderer->RenderCopy = SW_RenderCopy;
renderer->RenderCopyEx = SW_RenderCopyEx;
renderer->RenderReadPixels = SW_RenderReadPixels;
renderer->RenderPresent = SW_RenderPresent;
renderer->DestroyTexture = SW_DestroyTexture;
renderer->DestroyRenderer = SW_DestroyRenderer;
renderer->info = SW_RenderDriver.info;
renderer->driverdata = data;
SW_ActivateRenderer(renderer);
return renderer;
}与前面的函数一样，该函数完毕了SDL_Renderer结构体中函数指针的赋值。
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