Finding Pixel Color
I am trying to figure out how to extract the RGB value from the pixel chosen. Every time I click though, it gives me a value of 0, even though I am clicking on a colored triangle.
void mouse(int button, int state, int x, int y) {
if(state == GLUT_DOWN) {
开发者_高级运维 float mx = p2w_x(x); // pixel to world coordinates
float my = p2w_y(y);
float rgb[3];
glReadPixels(mx, my, 1, 1, GL_RGB, GL_FLOAT, rgb);
std::cout << rgb[0] << std::endl; // prints 0 for red always
}
}
I don't think you should convert the pixel coordinates to world coordinates. I don't know GL, but it looks wrong to me. You get pixel coordinates from the mouse right? And you want a pixel color value, from the framebuffer.
Maybe you could also use an integer type for color value, with GL_UNSIGNED_BYTE and an array of unsigned char rgb[3];
instead. And use GL_RGB8 for format, instead of just plain GL_RGB.
Also see how to set up the pixel format (store) of the frame buffer. This will affect subsequent glReadPixels calls.
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