WebGL之点上添加图片（using texture on point）

var VSHADER_SOURCE =[    
        "attribute vec4 a_Position;",                            
        "uniform mat4 u_ProjMatrix;",
        "uniform float u_PointSize;",
        "void main() {",
            "    gl_PointSize = u_PointSize;",
            "    gl_Position = u_ProjMatrix * a_Position;",
        "}"

    ].join("
")
var FSHADER_SOURCE =
[
        "precision mediump float;",    
        "uniform sampler2D u_Sampler;",               
        "void main() {",     
　　　　　"　　gl_FragColor = texture2D(u_Sampler,vec2(gl_PointCoord.x,1.0 - gl_PointCoord.y));",
        "}"

    ].join("
")

function main() {
    var canvas = document.getElementById('webgl');
    var gl = getWebGLContext(canvas);
    if (!gl) {
            console.log('Failed to get the rendering context for WebGL');
            return;
    }
    if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
            console.log('Failed to intialize shaders.');
        return;
    }  
    var projMatrix4=new Matrix4();
    projMatrix4.setOrtho(-1,1,-1,1,0.0,1.0);
    var u_projMatrix=gl.getUniformLocation(gl.program,'u_ProjMatrix');  
    gl.uniformMatrix4fv(u_projMatrix,false,projMatrix4.elements);    var position=gl.getAttribLocation(gl.program,'a_Position');
    gl.vertexAttrib3f(position,0.0,0.0,0.0);

    gl.clearColor(0, 0, 0, 1);
    gl.clear(gl.COLOR_BUFFER_BIT);
      
    loadImg(gl);

}
function loadImg(gl){
    var image=new Image();
    image.onload=function(){
        drawPic(gl,image)
    }
    image.src="pic.png";
}

function drawPic(gl,image){
    var width=image.width; 
    var height=image.height; 

    var pointSize=gl.getUniformLocation(gl.program,"u_PointSize");
    gl.uniform1f(pointSize,Math.max(width,height));
    
    var texture=gl.createTexture();
    //gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL,1);
    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D,texture);
    
    gl.texParameteri(gl.TEXTURE_2D,gl.TEXTURE_MAG_FILTER,gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D,gl.TEXTURE_MIN_FILTER,gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D,gl.TEXTURE_WRAP_S,gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D,gl.TEXTURE_WRAP_T,gl.CLAMP_TO_EDGE);
    
    gl.uniform1i(gl.getUniformLocation(gl.program,"u_Sampler"),0);
    gl.texImage2D(gl.TEXTURE_2D,0,gl.RGBA,gl.RGBA,gl.UNSIGNED_BYTE,image);
    gl.clear(gl.COLOR_BUFFER_BIT);
    gl.drawArrays(gl.POINTS,0,1);

    gl.bindTexture(gl.TEXTURE_2D, null);
}