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 上用 openGl 画一个实心圆?

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

我找到了许多解决方案，但没有一个有效.可能是因为有很多方法可以做到这一点.但是代码最短的方法是什么?

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

要获得真正平滑的圆，您将需要一个自定义片段着色器.例如下面的顶点着色器:

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正方形内绘制一个平滑的红色圆圈.您需要将正方形的顶点提供给 position 属性，并将 X 和 Y 的坐标范围从 0.0 到 1.0 提供给 inputTextureCoordinate 属性，但这会绘制一个圆在视口分辨率允许的范围内锐利，而且速度非常快.

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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