How to pass one float as four unsigned chars to shader by glVertexPointAttrib?

Posted by Kog on Game Development See other posts from Game Development or by Kog
Published on 2012-11-22T13:13:00Z Indexed on 2012/11/22 17:12 UTC
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For each vertex I use two floats as position and four unsigned bytes as color. I want to store all of them in one table, so I tried casting those four unsigned bytes to one float, but I am unable to do that correctly...

All in all, my tests came to one point:

    GLfloat vertices[] = { 1.0f, 0.5f, 0, 1.0f, 0, 0 };
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float),
        vertices);

// VER1 - draws red triangle
//  unsigned char colors[] = { 0xff, 0, 0, 0xff, 0xff, 0, 0, 0xff, 0xff, 0, 0,
//          0xff };
//  glEnableVertexAttribArray(1);
//  glVertexAttribPointer(1, 4, GL_UNSIGNED_BYTE, GL_TRUE, 4 * sizeof(GLubyte),
//          colors);

// VER2 - draws greenish triangle (not "pure" green)
//  float f = 255 << 24 | 255; //Hex:0xff0000ff
//  float colors2[] = { f, f, f };
//  glEnableVertexAttribArray(1);
//  glVertexAttribPointer(1, 4, GL_UNSIGNED_BYTE, GL_TRUE, 4 * sizeof(GLubyte),
//          colors2);

// VER3 - draws red triangle
int i = 255 << 24 | 255; //Hex:0xff0000ff
int colors3[] = { i, i, i };
glEnableVertexAttribArray(1);
glVertexAttribPointer(1, 4, GL_UNSIGNED_BYTE, GL_TRUE, 4 * sizeof(GLubyte),
        colors3);

glDrawArrays(GL_TRIANGLES, 0, 3);

Above code is used to draw one simple red triangle. My question is - why do versions 1 and 3 work correctly, while version 2 draws some greenish triangle? Hex values are one I read by marking variable during debug. They are equal for version 2 and 3 - so what causes the difference?

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