geometry shader

What differentiates the geometry shader from the other shaders?

• Vertex and pixel shaders get one vertex at a time, but the geometry shader operates on the entire primitive (3 or 4 vertices) at once.

• Vertex/pixel are fixed output/input (turn one data into another), geometry shader is variable output/input (can create new vertice, do smth with triangle, whatever)

T/F: Geometry shader is optional

True

Geometry shader is the last shader before…

rasterizer

T/F: Geometry shader improves line-on-polygon shading

True, this helps get rid of z-fighting

What is possible when a single primitive can access its neighbors? What makes this possible?

Geometry shader allows for cartoon shading and silhouette edge shading

T/F: Geometry shader provides information to the pixel shader

True

What is quad split? Issues with it? Solution?

A quadrilateral has diagonal drawn through it and rasterized as two triangles, and each part is rendered separately.

Get shading/texture artifacts (doesn’t look continuous) because edges of the object can become degenerate (i.e. the tip of a cone, all the edges are squashed together)

• surface normals at tip are also irregular/almost undefined

Solution: Use geometry shader to get all 4 vertices at same time (quad is a quad rather than 2 separate triangles) to apply barycentric coordinates