Why this code print white rectangle instead of red in OpenGL? - c++

Question

I am doing some test with opengl and trying to draw a red rectangle. This is the code:
qDebug(__FUNCTION__);
float *rgbImage = (float *)malloc(width * height * 3 * sizeof(float));
float *rgbImagePtr = rgbImage;
qDebug("Initializing");
int y, x;
for(y = 0; y < height; y++)
{
for(x = 0; x < width; x++)
{
*rgbImagePtr++ = 255; // R
*rgbImagePtr++ = 0; // G
*rgbImagePtr++ = 0; // B
}
}
// Generate false image
qDebug("Creating texture");
GLuint texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
qDebug("drawing image");
glTexImage2D(GL_TEXTURE_2D, 0, 3, width, height, 0, GL_RGB, GL_FLOAT, rgbImage);
qDebug("drawing image finished");
When I run my example, I get white rectangle instead of red as I figure out when I am doing. What's the issue?
EDIT 1
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f); glVertex3f( 0.0f, 0.0f, 0.0f);
glTexCoord2f(1.0f, 0.0f); glVertex3f(256.0f, 0.0f, 0.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3f(256.0f, 256.0f, 0.0f);
glTexCoord2f(0.0f, 1.0f); glVertex3f( 0.0f, 256.0f, 0.0f);
glEnd();
Draw code added

Answer 1

Most likely the problem is, that your texture is considered incomplete due to the lack of mipmap layers. You either have to turn off mipmapping for the texture or supply a full stack of mipmap layers.
Additionally it seems you didn't enable the GL_TEXTURE_2D target on the active texture unit (required if using the fixed function pipeline).

Answer 2

The call to glTexImage2d has an incorrect internalFormat parameter:
glTexImage2D(GL_TEXTURE_2D, 0, 3, width, height, 0, GL_RGB, GL_FLOAT, rgbImage);
^-- here
The documentation says that it specifies number of color components in the texture, but it also says that the value should one of the enums given at the end of the page.
In your, case instead of 3, it should be GL_RGB.