2

I am executing the following, which I have derived from a few different tutorials (Just a single render pass, initialisation code not shown but works fine for untextured primitives):

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrthof(0, xSize, 0, ySize, -1.0f, 1.0f);
glMatrixMode(GL_MODELVIEW);

glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
glEnable(GL_TEXTURE_2D);
glBlendFunc(GL_ONE, GL_SRC_COLOR);

GLuint texture[1];
glGenTextures(1, &texture[0]);
glBindTexture(GL_TEXTURE_2D, texture[0]);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);

int width = 50;
int height = 50;
void* textureData = malloc(width * height * 4);
CGColorSpaceRef cSp = CGColorSpaceCreateDeviceRGB();
CGContextRef ct = CGBitmapContextCreate(textureData, width, height, 8, width*4, cSp, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGContextSetRGBFillColor(ct, 0, 1, 0, 1);
CGContextFillRect(ct, CGRectMake(0, 0, 50, 50));
CGContextRelease(ct);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData);

float verts[] = {
0.0f, 0.0f, 0.0f,
50.0f, 0.0f, 0.0f,
0.0f, 50.0f, 0.0f,
50.0f, 50.0f, 0.0f
};

float texCords[] = {
0.0f, 0.0f,
1.0f, 0.0f,
0.0f, 1.0f,
1.0f, 1.0f
};

 glVertexPointer(3, GL_FLOAT, 0, verts);
 glTexCoordPointer(2, GL_FLOAT, 0, texCords);
 glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

 glDisable(GL_TEXTURE_2D);

The result is a white square. Not the green one as intended. Can anyone spot the error(s) in my code which result in its' failure to render?

I hope to get this working then move it on to text rendering.

genpfault
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Toby Wilson
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  • Should probably say, I know the above even if it did work is horribly inefficient, and that some of it shouldn't even be in the render loop. It's just for the sake of simplicity and getting it working. – Toby Wilson Apr 26 '10 at 13:45

1 Answers1

3

The problem is that width and height are not powers of two. There are two solutions:

  • Use the texture rectangle extension. Set the texture target to GL_TEXTURE_RECTANGLE_ARB instead of GL_TEXTURE_2D. You will have to enable this extension before using it. Note that rectangle textures do not support mipmaps.
  • Use powers of two for texture dimensions.
Dietrich Epp
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