Projection & the Frustum
See the camera’s frustum as an object in the world, and the picture it produces, side by side.
What you should come away with: What the perspective divide actually does, and why near and far are a hard clip rather than a fade.
World · the frustum from outside
- frustum
- kept
- clipped
Camera · what it renders
The projection matrix
| 1.340 | 0.000 | 0.000 | 0.000 |
| 0.000 | 2.145 | 0.000 | 0.000 |
| 0.000 | 0.000 | -1.316 | -3.474 |
| 0.000 | 0.000 | -1.000 | 0.000 |
The −1 in the bottom row is the whole trick. It copies −z into w, and the divide the GPU performs after your vertex shader — x/w, y/w — is what makes distant things small. Switch to orthographic and that entry becomes 0: w stays 1, nothing shrinks.