CIS 565 Project 4: CUDA Rasterizer

• Kai Ninomiya (Arch Linux/Windows 8, Intel i5-4670, GTX 750)

Base Code Features

• A library for loading/reading standard Alias/Wavefront .obj format mesh files and converting them to OpenGL style VBOs/IBOs
• A suggested order of kernels with which to implement the graphics pipeline
• Working code for CUDA-GL interop

Features Implemented

• Vertex shader
  • Model-view-projection transformation
• Primitive Assembly with support for triangle VBOs/IBOs
• Geometry shader
  • Maps 1 triangle to 0-4 triangles.
  • Backface culling (somewhat more efficient than culling in the rasterization step).
• Basic scanline rasterization into a fragment buffer
  • Depth-testing
  • Barycentric interpolation of vertex data
    • Color: not visible on uncolored model
    • Normals: visible with suzanne.obj model
    • World-space position: used in lighting calculations
  • Using atomicMin to avoid race conditions in depth testing
• Fragment shading
  • Lambert diffuse per-fragment lighting
• Fragment to framebuffer writing

(Extras in bold.)

Renderings

Diffuse shading:

Diffuse shading showing normal interpolation:

Tessellation in geometry shader:

Feature Performance

Feature	Frame time	Added time	Added time	Notes
Nothing	4.17 ms			Base code.
Prim asm	4.22 ms	0.05 ms	1.20%	Copying data, handling IBO.
Rast+render	4.77 ms	0.55 ms	13.03%	No locking.
Normal buffer	4.84 ms	0.07 ms	1.47%	Using normals from mesh.
Basic frag shad	5.80 ms	0.96 ms	19.83%	Renders model normals.
Backface cull	5.76 ms	-0.04 ms	-0.69%	6.13ms using stream compaction to remove backfaces
Vert/frag structs	5.78 ms	0.02 ms	0.35%	Performance drop statistically insignificant.
World-space pos	7.21 ms	1.43 ms	24.74%	Extra fragment input, extra interpolation of that input.
Depth buf optim	7.13 ms	-0.08 ms	-1.11%	Remove some unnecessary depth checks.
VS transforms	7.77 ms	0.64 ms	8.98%	Note that the change in screen size of the model affects the performance.
Lambert shading	8.29 ms	0.52 ms	6.69%
GS w/ compaction	8.82 ms	0.53 ms	6.39%	Maximum 4 output tris per input tri. Stream compaction is used after this stage.
Tessellation GS	8.66 ms	-0.16 ms	-1.81%	Splits each tri into 3 tris, colors one red.
GS w/ compaction	9.69 ms			(This series of runs gave overall different results since I did them at a different time.)
GS w/o compaction	8.57 ms	-1.12 ms	-11.56%
Tessellation GS	8.12 ms	-0.45 ms	-5.25%	Tessellation reduces the number of wasted iterations in the rasterization step by decreasing the number of rasterized pixels outside of triangles.
Backface GS	7.91 ms	-0.21 ms	-2.59%	Moved backface culling to inside the GS. This performs a bit better and benefits from the stream compaction already being done for the GS stage.

Stream compaction seems to be quite costly. With tessellation, only about 1/2 of the triangles would be removed. The performance drop without tessellation is less sharp, since it removes 7/8 of the triangles; but compaction still doesn't improve overall performance.

	With tessellation	Without tessellation
Without compaction	7.91 ms	9.48 ms
With compaction	9.17 ms	8.57 ms

Tile size performance

Tile size	Frame time
16	9.50 ms
32	9.17 ms
64	9.19 ms
128	9.27 ms

Debug/Progress Renderings (chronological)

Rasterization test:

Depth buffer test (no locks):

Face normals:

Backface culling (reduces flickering due to race conditions):

World-space positions: