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Culling
After the space transformation, several tests are applied onto the polygon to determine if it is visible on the screen. These tests are:
- Back-face culling: removes polygons facing away from the viewer
- Frustum culling: Test if the polygon is outside the camera view
The back-face culling allows to removes the polygons (faces) that are not visible to the camera.
The polygon orientation is determined by checking the vertices, which are defined in a specific order, typically counter-clockwise for front-facing polygons. If the face is pointing away from the camera, it is discarded, as it is obscured by other faces and would not be visible.
If the polygon passed the back-face culling, it is tested to determine if it is contained inside the camera view.
As the polygon was already transformed to the screen coordinates, the resulting triangle bounding box may be calculated. If this bounding box is contained on the frame canvas, the polygon is visible. Otherwise it is discarded.