Hi you can either simply load your image into a shader and in it use some specific logic for “copying” the pixels. You can use an ofFbo to render the shader so you then can use re use on the next drawing cycle.
If you simply want to draw it you can draw the texture several times with different subsections.
you can use
ofImage's following function
/// \param x X position to draw cropped image at.
/// \param y Y position to draw cropped image at.
/// \param w Width of subsection to draw.
/// \param h Height of subsection to draw.
/// \param sx X position in image to begin cropping from.
/// \param sy Y position in image to begin cropping from.
void drawSubsection(float x, float y, float w, float h, float sx, float sy) const;
Last thing you can do is simply access the array of data and copy (even using a
memcpy, which can be a bit scary if you dont know exactly whats going on)
//define an area to copy by a rectangle in the number below!
int x ;
img.getPixels().cropTo(imgBlock.getPixels(),x,y, w, h);
//or instead you can go much nastier and do a memcpy, but I am a bit tired now to think on the right indices to use. hope this is helpful