OpenGL: Keep drawing inside a region on a plane in 3D space

Question

Step 1: I use glVertex() to draw a shape, say a rectangle, in 3D space.

Step 2: I then draw things inside this rectangle - for example with glutStrokeCharacter() and with glVertex() again.

I need to keep what are drawn in step 2 inside the rectangle drawn in step 1, clipping away anything that goes outside the boundary. Can someone give some hint on how to do this?

Answer 1

1. Render bounding geometry into stencil buffer.
2. Enable stencil test
3. Render regular geometry into color buffer; the stencil test will prevent fragments outside the bounding geometry from writing to the color buffer.