Question

I’ve got a screen-aligned quad, and I’d like to zoom into an arbitrary rectangle within that quad, but I’m not getting my math right.

I think I’ve got the translate worked out, just not the scaling. Basically, my code is the following:

//
// render once zoomed in
glPushMatrix();
glTranslatef(offX, offY, 0);
glScalef(?wtf?, ?wtf?, 1.0f);

RenderQuad();

glPopMatrix();

//
// render PIP display
glPushMatrix();
glTranslatef(0.7f, 0.7f, 0);
glScalef(0.175f, 0.175f, 1.0f);

RenderQuad();

glPopMatrix();

Anyone have any tips? The user selects a rect area, and then those values are passed to my rendering object as [x, y, w, h], where those values are percentages of the viewport’s width and height.

Answer 1

When I’ve needed to do this, I’ve always just changed the parameters I passed to glOrtho, glFrustrum, gluPerspective, or whatever (whichever I was using).