从渲染缓冲区 webgl2 读取像素

Question

如何从 webgl2 中的渲染缓冲区读取像素？ 我试过下面的代码，但我只得到零（0、0、0 ...），除了红色和 alpha 不为零

    const targetTexture = gl.createTexture();
    gl.bindTexture(gl.TEXTURE_2D, targetTexture);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, width, height, 0, gl.RGBA, gl.UNSIGNED_BYTE, null);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_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);

    const frameBuf = gl.createFramebuffer()!;
    gl.bindFramebuffer(gl.FRAMEBUFFER, frameBuf);
    gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, targetTexture, 0);

    const depthBuf = gl.createRenderbuffer();
    gl.bindRenderbuffer(gl.RENDERBUFFER, depthBuf);
    gl.renderbufferStorage(gl.RENDERBUFFER, gl.DEPTH_COMPONENT16, 512, 512);
    gl.framebufferRenderbuffer(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.RENDERBUFFER, depthBuf);

    const colorBuf = gl.createRenderbuffer();
    gl.bindRenderbuffer(gl.RENDERBUFFER, colorBuf);
    gl.renderbufferStorage(gl.RENDERBUFFER, gl.RGBA4, 512, 512);
    gl.framebufferRenderbuffer(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.RENDERBUFFER, colorBuf);

    gl.viewport(0, 0, 512, 512);
    gl.clearColor(1.0, 0.0, 0.0, 1.0);
    gl.clearDepth(1.0);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    const results = new Uint8Array (512 * 512 * 4);
    gl.readPixels(0, 0, 512, 512, gl.RGBA, gl.UNSIGNED_BYTE, results);
    console.log(results)

Answer 1

所以看来我发布的代码确实有效。 问题是我也在使用gl.SCISSOR_TEST （上面的代码中没有包含）并禁用它似乎可以解决我的问题。