OpenGL ES 2.0 Convert int[] to GLubyte[] - opengl-es

Question

The following works as a texture...
GLubyte bytePix[4 * 3] ={
255, 0, 0, //red
0, 255, 0, //green
0, 0, 255, //blue
255, 255, 0 //yellow
};
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, pixelWidth, pixelHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, pbytePix);
Problem is I am passing in my BMP as an int[] so I would need something more like this...
int bytePix[4 * 3] ={
255, 0, 0, //red
0, 255, 0, //green
0, 0, 255, //blue
255, 255, 0 //yellow
};
But this doesn't show the same result.
My question is how do I convert the latter into a GLubtye[] or some other recognizable format.

Answer 1

On your platform, sizeof(int) clearly isn't equal to sizeof(GLubyte). I guess the immediate question is — why are you using int? It's likely just to be a huge waste of space if you're storing only values in the range 0–255.
You can't just use GL_INT or GL_UNSIGNED_INT in place of GL_UNSIGNED_BYTE, even if they are the same size as your int as you're using only a byte's range within each integer.
That aside, you'll notice that glTexImage2D doesn't have a stride parameter unlike glVertexAttribPointer and most of the other functions that exist primarily to provide data. So even though you have your values within bytes and those bytes are a predictable space apart, OpenGL can't pull them apart and repack them for you.
So the easiest option is to do it yourself:
void glTexImage2DWithStride(..., GLsizei stride, ...)
{
// the following is written to assume GL_RGB; adapt as necessary
GLubyte *byteBuffer = (GLubyte *)malloc(width * height * 3);
for(int c = 0; c < width * height * 3; c++)
byteBuffer[c] = originalBuffer[c];
glTexImage2D(..., byteBuffer, ...);
free(byteBuffer);
}
Failing that, supposing your int is four times as large as a byte, you could upload the original as an RGBA texture that's four times as large as its real size, then shrink it down in a shader, combining the .r or .as (as per your endianness) into the correct output channels.

Answer 2

Since ubyte and int are different in size, I guess you have to create a new ubyte array and convert explicitly element by element with a for loop, before passing it to OpenGL.