CorePlot学习 坐标轴的详细分析

    //坐标轴的初始化  
    -(void)axesInit  
    {  
        // Setup plot space: 设置一屏内可显示的x,y量度范围  
        CPTXYPlotSpace *plotSpace = (CPTXYPlotSpace *)[xyGraph defaultPlotSpace];  
        plotSpace.delegate = self;  
        plotSpace.allowsUserInteraction = YES;//允许拖动  
        //设置移动时的停止动画  这些参数保持默认即可  变化不大  
        plotSpace.momentumAnimationCurve = CPTAnimationCurveCubicIn;  
        plotSpace.bounceAnimationCurve = CPTAnimationCurveBackIn;  
        plotSpace.momentumAcceleration = 20000.0;  
        //设置x,y在视图显示中大小，也就是点的个数，通过这样设置可以达到放大缩小的效果，来达到我们想要的合理视图显示  
        plotSpace.xRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(18.0) length:CPTDecimalFromFloat(22.0)];  
        plotSpace.yRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(32.0) length:CPTDecimalFromFloat(10.5)];  
        //设置x、y轴的滚动范围，如果不设置，默认是无线长的  
         plotSpace.globalXRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(-1.0) length:CPTDecimalFromFloat(25.0)];  
        plotSpace.globalYRange = [CPTPlotRange plotRangeWithLocation:CPTDecimalFromFloat(32.0) length:CPTDecimalFromFloat(10.5)];  
        // Axes: 设置x,y轴属性，如原点，量度间隔，标签，刻度，颜色等  
        CPTXYAxisSet *axisSet = (CPTXYAxisSet *)xyGraph.axisSet;  
        CPTMutableLineStyle *lineStyle = [CPTMutableLineStyle lineStyle];  
        lineStyle.miterLimit = 1.0f;  
        lineStyle.lineWidth = 1.0f;  
        lineStyle.lineColor = [CPTColor whiteColor];  
          
        [plotSpace setAllowsMomentumX:YES];  
          
        CPTXYAxis *x = axisSet.xAxis;  
          
        x.orthogonalCoordinateDecimal = CPTDecimalFromString(@"33");// x轴的原点位置，其实这里是y坐标的值，也就是说x轴的原点在y轴的1位置  
          
        x.majorIntervalLength = CPTDecimalFromString(@"1.0");  // x轴主刻度：显示数字标签的量度间隔  
          
        x.minorTicksPerInterval  = 4;  // x轴细分刻度：每一个主刻度范围内显示细分刻度的个数  
          
        x.minorTickLineStyle = lineStyle;  
          
        lineStyle.lineColor = [CPTColor lightGrayColor];  
        x.majorGridLineStyle = lineStyle;//这里设置x轴中主刻度的栅格，平行于y轴  
        // 需要排除的不显示数字的主刻度  
        NSArray *exclusionRanges = [NSArray arrayWithObjects:  
                                    [self CPTPlotRangeFromFloat:0.99 length:0.02],  
                                    [self CPTPlotRangeFromFloat:2.99 length:0.02],  
                                    nil nil];  
        x.labelExclusionRanges = exclusionRanges;  
          
        CPTXYAxis *y = axisSet.yAxis;  
        y.orthogonalCoordinateDecimal = CPTDecimalFromString(@"18");//y轴的原点位置，其实这里是x坐标的值，也就是说y轴的原点在x轴的0位置  
        //固定y轴，也就是在你水平移动时，y轴是固定在左/右边不动的，以此类推x轴  
        y.axisConstraints = [CPTConstraints constraintWithLowerOffset:20];//这里是固定y坐标轴在最右边（距离可视右边界有20个像素距离，一遍显示标签）  
          
        y.majorIntervalLength = CPTDecimalFromString(@"0.5");  
        y.minorTicksPerInterval = 4;  
        y.minorTickLineStyle = lineStyle;  
          
        y.tickDirection = CPTSignNegative;//标签的方向，对于y轴来说：CPTSignPositive标签在y轴的右边，CPTSignNegative：在y轴的左侧  
          
        lineStyle.lineColor = [CPTColor lightGrayColor];  
        y.majorGridLineStyle = lineStyle;//设置栅格线，平行于x轴   如果 labelingPolicy 设置为 CPTAxisLabelingPolicyNone ， majorGridLineStyle 将不起作用  
        // y.labelingPolicy = CPTAxisLabelingPolicyNone;  
        NSArray *exclusionRangesY = [NSArray arrayWithObjects:  
                                     [self CPTPlotRangeFromFloat:1.99 length:0.2],  
                                     [self CPTPlotRangeFromFloat:2.99 length:0.2], nil nil];  
        y.labelExclusionRanges = exclusionRangesY;  
        y.delegate = self;  
          
    }  

    /** @brief Creates and returns a new CPTConstraints instance initialized with a fixed offset from the lower bound. 
     *  @param newOffset The offset. 
     *  @return A new CPTConstraints instance initialized with the given offset. 
     *  @sfx :该函数主要是实现固定坐标轴在距离最小端newoffset的地方，我个人对大端小端的理解：对y轴来说，最大端（或者说最高处）也就是我们坐标系bounce的右边界 
     *        最小端（或者说最低处）就是坐标系视图boundce的左边界，这样x轴也就同样可以理解了，相应的就是上、下边界 
     **/  
    +(CPTConstraints *)constraintWithLowerOffset:(CGFloat)newOffset  
    {  
        return [[(_CPTConstraintsFixed *)[_CPTConstraintsFixed alloc] initWithLowerOffset : newOffset] autorelease];  
    }  
    <pre name="code" class="objc">/** @brief Creates and returns a new CPTConstraints instance initialized with a fixed offset from the upper bound. 
     *  @param newOffset The offset. 
     *  @return A new CPTConstraints instance initialized with the given offset. 
     *  @sfx :该函数主要是实现固定坐标轴在距离最高端newoffset的地方，我个人对大端小端的理解：对y轴来说，最大端（或者说最高处）也就是我们坐标系bounce的右边界 
     *        最小端（或者说最低处）就是坐标系视图boundce的左边界，这样x轴也就同样可以理解了，相应的就是上、下边界 
     **/  
    +(CPTConstraints *)constraintWithUpperOffset:(CGFloat)newOffset{   
        return [[(_CPTConstraintsFixed *)[_CPTConstraintsFixed alloc] initWithUpperOffset : newOffset] autorelease];  
    }  
    /** @brief Creates and returns a new CPTConstraints instance initialized with a proportional offset relative to the bounds.  
    * * For example, an offset of @num{0.0} will return a position equal to the lower bound, @num{1.0} will return the upper bound,  
    * and @num{0.5} will return a point midway between the two bounds.  
    * * @param newOffset The offset. 
    * @sfx ： 这个类方法实现的是按一定比例值来固定坐标轴，比如我们固定y轴，如果newoffset = 1.0，就相当于把y轴固定在右边界，如果newoffset = 0.0 就是左边界，如果等于0.5就是中间 
    newoffset取值范围：0 --- 1.0 
     * @return A new CPTConstraints instance initialized with the given offset.  
    **/  
    +(CPTConstraints *)constraintWithRelativeOffset:(CGFloat)newOffset{   
        return [[(_CPTConstraintsRelative *)[_CPTConstraintsRelative alloc] initWithRelativeOffset : newOffset] autorelease];  
    }