<p>I have image data and i want to get a sub image of that to use as an opengl texture. </p>

<pre><code>glGenTextures(1, &amp;m_name);
glGetIntegerv(GL_TEXTURE_BINDING_2D, &amp;oldName);
glBindTexture(GL_TEXTURE_2D, m_name);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_width, m_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_data);
</code></pre>

<p>How can i get a sub image of that image loaded as a texture. I think it has something to do with using glTexSubImage2D, but i have no clue how to use it to create a new texture that i can load. Calling: </p>

<pre><code>glTexSubImage2D(GL_TEXTURE_2D, 0, xOffset, yOffset, xWidth, yHeight, GL_RGBA, GL_UNSIGNED_BYTE, m_data);
</code></pre>

<p>does nothing that i can see, and calling glCopyTexSubImage2D just takes part of my framebuffer.
Thanks</p>

Edit:
Use glPixelStorei. You use it to set
```
GL_UNPACK_ROW_LENGTH
```
to the width (in pixels) of the entire image. Then you call glTexImage2D (or whatever), passing it a pointer to the first pixel of the subimage and the width and height of the subimage.
Don't forget to restore
```
GL_UNPACK_ROW_LENGTH
```
to 0 when you're finished with it.
Ie:
```
```
glPixelStorei( GL_UNPACK_ROW_LENGTH, img_width );
char *subimg = (char*)m_data + (sub_x + sub_y*img_width)*4;
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, sub_width, sub_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, subimg );
glPixelStorei( GL_UNPACK_ROW_LENGTH, 0 );
```
```
Or, if you're allergic to pointer maths:
```
```
glPixelStorei( GL_UNPACK_ROW_LENGTH, img_width );
glPixelStorei( GL_UNPACK_SKIP_PIXELS, sub_x );
glPixelStorei( GL_UNPACK_SKIP_ROWS, sub_y );

glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, sub_width, sub_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_data );

glPixelStorei( GL_UNPACK_ROW_LENGTH, 0 );
glPixelStorei( GL_UNPACK_SKIP_PIXELS, 0 );
glPixelStorei( GL_UNPACK_SKIP_ROWS, 0 );
```
```
Edit2:
For the sake of completeness, I should point out that if you're using OpenGL-ES then you don't get
```
GL_UNPACK_ROW_LENGTH
```
. In which case, you could either (a) extract the subimage into a new buffer yourself, or (b)...
```
```
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, sub_width, sub_height, 0, GL_RGBA, GL_UNSIGNED_BYTES, NULL );

for( int y = 0; y < sub_height; y++ )
{
    char *row = m_data + ((y + sub_y)*img_width + sub_x) * 4;
    glTexSubImage2D( GL_TEXTURE_2D, 0, 0, y, sub_width, 1, GL_RGBA, GL_UNSIGNED_BYTE, row );
}
```
```