如何在iPhone上使用OpenGL ES绘制实心圆？ [英] How do I draw a filled circle with OpenGL ES on iPhone?

问题描述

如何在iPhone上使用openGl绘制一个实心圆圈？

How do I draw a filled circle with openGl on iPhone ?

我找到了很多解决方案，但没有一个能够正常工作。可能是因为有很多方法可以做到这一点。但是用最短代码的方法是什么？

I've found many solutions but none of them work. Probably because there are many ways to do it. But what's the method with shortest code ?

推荐答案

对于一个真正流畅的圆圈，你将需要一个自定义片段着色器。例如，以下顶点着色器：

For a truly smooth circle, you're going to want a custom fragment shader. For example, the following vertex shader:

 attribute vec4 position;
 attribute vec4 inputTextureCoordinate;

 varying vec2 textureCoordinate;

 void main()
 {
    gl_Position = position;
    textureCoordinate = inputTextureCoordinate.xy;
 }

和片段着色器：

 varying highp vec2 textureCoordinate;

 const highp vec2 center = vec2(0.5, 0.5);
 const highp float radius = 0.5;

 void main()
 {
     highp float distanceFromCenter = distance(center, textureCoordinate);
     lowp float checkForPresenceWithinCircle = step(distanceFromCenter, radius);

     gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0) * checkForPresenceWithinCircle;     
 }

将在您绘制到屏幕的方块内绘制一个平滑的红色圆圈。您需要为您的方块提供顶点到位置属性，并在X和Y中将坐标范围从0.0到1.0到 inputTextureCoordinate 属性，但这将绘制一个与视口分辨率允许的一样清晰的圆圈，并且非常快速地完成。

will draw a smooth red circle within a square that you draw to the screen. You'll need to supply vertices for your square to the position attribute and coordinates that range from 0.0 to 1.0 in X and Y to the inputTextureCoordinate attribute, but this will draw a circle that's as sharp as your viewport's resolution allows and do so very quickly.

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