Technical Explanation of Ramp Creation in Quake's Level Editor

To create diagonal surfaces from the rectangular brush we would place two points that could slice any geometry that the line between them intersected.

Every angle in the game was made this way.

For example, on E1M1 (the first level), you step off the slipgate and go down a ramp to the first hallway.

To create that ramp I dragged a brush that was left-to-right the length of the ramp, and top-to-bottom the height of the ramp.

Keep in mind, I'm working in a view that is looking straight down into the level from above, so I'm creating a ramp in a different rotation than it should be.