java - glReadPixels 返回错误值

Question

我尝试获取渲染像素的颜色。

gl.glColor3f(1f, 0, 0);
//draw
gl.glReadPixels(lastX - pw / 2, MyCanvas.this.getHeight()
            - (lastY - ph / 2), pw, ph, GL.GL_RED, GL.GL_FLOAT,
            pixelBuffer);
float r, g, b;
r = pixelBuffer.getFloat();
g = pixelBuffer.getFloat();
b =pixelBuffer.getFloat();
pixelBuffer.rewind();
System.out.println(r+" "+g+" "+b);

屏幕上出现了真正的纯红色，但是glReadPixels返回的r值很奇怪4.6006E-41，为什么？？？

Answer 1

glReadPixels documentation说:

Storage parameters set by glPixelStore, such as GL_PACK_LSB_FIRST and GL_PACK_SWAP_BYTES, affect the way that data is written into memory.

因此请检查您的glPixelStore 配置。也就是说，您的字节顺序是向后的。

0x0000803F => 4.600602988224807e-41
0x3F800000 => 1.0

有用的链接:

• http://babbage.cs.qc.edu/IEEE-754/Decimal.html
• http://babbage.cs.qc.edu/IEEE-754/32bit.html