webgl readpixels总是返回0,0,0,0 [英] webgl readpixels is always returning 0,0,0,0

问题描述

我正在尝试在WebGl中进行选择。我有两个渲染的形状，每个都映射了不同的纹理。我试图在某些坐标上抓取像素。以下是示例。

I am trying to do picking in WebGl. I have two shapes rendered along with different texture mapped on each. I am trying to grab pixel on certain co-ordinates. Here is the example.

var pixelValues = new Uint8Array(4);
gl.readPixels(10, 35, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixelValues);
console.log(pixelValues);

但是pixelValues总是包含[0,0,0,0]。我究竟做错了什么？我是否需要做一些与帧缓冲相关的事情？

But pixelValues always contain [0,0,0,0]. What am I doing wrong? Do I need to do something related to framebuffer?

推荐答案

根据 WebGL最新规范，你现在需要调用 getContext 设置 preserveDrawingBuffer flag，如：

According to WebGL latest specs, you now need to call getContext setting the preserveDrawingBuffer flag, like:

var ctx = canvas.getContext("experimental-webgl", {preserveDrawingBuffer: true});

这可以防止绘图缓冲区（颜色，深度，模板）在绘制到屏幕后被清除。请记住，这可能会导致性能下降。

this prevents the drawing buffer (color, depth, stencil) from being cleared after they are draw to screen. Keep in mind that settings this may cause a performance penalty.

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