Creating texture from RGB - qt

Question

I am receiving an screen-shot Palette over the network. Next, I convert the Palette indices to their relevant RGB using my matrix containing different colors.
The problem I have with the code is I cannot create a texture out of this RGB image I receive successfully.
oid GlWidget::createTextureFromBitmap(QByteArray btmp)
{
tex.buf = new unsigned char[bytes.size()];
memcpy(tex.buf, bytes.constData(), bytes.size());
glGenTextures( 1, &tex.id);
glBindTexture(GL_TEXTURE_2D, tex.id);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_LINEAR_MIPMAP_LINEAR);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGB, 0, 0, 0, GL_RGB, GL_UNSIGNED_BYTE, tex.buf);
gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGB, 800, 600, GL_RGB, GL_UNSIGNED_BYTE, tex.buf);
delete [] tex.buf;
tex.buf = NULL;
updateGL();
}
void GlWidget::paintGL()
{
shaderProgram.bind();
shaderProgram.setUniformValue("mvpMatrix", pMatrix * vMatrix * mMatrix);
shaderProgram.setUniformValue("texture", 0);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex.id);
//glActiveTexture(0);
shaderProgram.setAttributeArray("vertex", vertices.constData());
shaderProgram.enableAttributeArray("vertex");
shaderProgram.setAttributeArray("textureCoordinate", textureCoordinates.constData());
shaderProgram.enableAttributeArray("textureCoordinate");
glDrawArrays(GL_TRIANGLES, 0, vertices.size());
shaderProgram.disableAttributeArray("vertex");
shaderProgram.disableAttributeArray("textureCoordinate");
shaderProgram.release();
}

Answer 1

glTexImage2D( GL_TEXTURE_2D, 0, GL_RGB, 0, 0, 0, GL_RGB, GL_3_BYTES, tex.buf);
gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGB, 800, 600, GL_RGB, GL_3_BYTES, tex.buf);
GL_3_BYTES is not a valid data type here, you prpbably mean GL_UNSIGNED_BYTE. Apart from that, there are some redundant calls here. Your glTexImage2D call will specify the data for mipmap level 0, the gluBuild2DMipmaps will specify all the mipmap levels, including 0. Since you use mipmapping, you will only need the latter of those calls. But both calls will fail with GL_INVALID_ENUM due to the wrong data type, so you don't have any texture. So you can replace that two lines by:
gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGB, 800, 600, GL_RGB, GL_UNSIGNED_BYTE, tex.buf);
Another thing:
glActiveTexture(0);
this is also invalid. Only the GL_TEXTUREn values are valid for that call. You also do not need to "disable" the active texture selector, as you might try to do here. It will always point to some valid texture unit.

Answer 2

In addition to the fixes mentioned above, you can improve the performance by not having to do an additional memcopy (1 in your code, 1 in GL driver), by sending the palette also as a texture, then doing the same indexing that you are doing in the CPU code, inside the shader code. Also, if you are anyway setting the bytes[] array, no need to clear the array first.