gerridae

the composite

hologram traces what light has to be right on. gerridae draws everything else: the room, the furniture and anything that moves. The two meet per pixel, by depth.

Two rasterized cubes in a traced room: a teal cube behind a grey polarizer, and an orange cube half inside a clear glass ball on a checker floor

m1: two cubes in a traced room

The cubes are rasterized; the floor, the ball, the pane and the polarizer are traced. The teal cube shows through the polarizer at half, by Malus. The orange cube shows through the thin pane at 96%, by Fresnel. Inside the ball it vanishes, because a ray the glass has bent has left the eye's line, and the raster has no image along it.

how the two meet

gerridae draws first, into a floating-point target the size of the framebuffer: linear radiance in rgb, and in alpha the path length from the eye to the surface it drew. hologram's tracer reads that per pixel as a cap and stops every ray still on the eye's line at it. If something traced is nearer, the tracer shades it as always. If not, the pixel takes the raster's colour, times whatever the ray picked up on the way.

"Still on the eye's line" is the primary ray and anything that carried on without turning: through a polarizer, a waveplate or a thin glass pane. So a mesh behind a pane shows through it by Fresnel, and behind a polarizer it obeys Malus, with no extra pass.

the oracle still holds

hologram's oracle reads the raster target back, hands it to the CPU tracer as per-pixel caps, and compares the whole presented frame at hologram's usual bars. That checks every traced pixel, every pixel the raster won, and the pane and polarizer arithmetic on the way. An oracle that ignores the caps fails the same frame, which is what makes the pass mean something.

m1_composite --diff              DIFF OK, mean 0.1042/255, 0.067% off
m1_composite --diff --spectral   DIFF OK, mean 0.0351/255, 0.139% off

milestones

It is at the first. The rest are planned.

MilestoneWhat it adds

m1The composite proof: one shape, a unit cube, on D3D11, held to the oracle.

m2Blender meshes, read from daffodil's prop format.

m3, m4Meshes in mirrors, starting with flat ones.

m5, m6Animation.

about

A mesh rasterizer for hologram by magmacrunch media. C99 on sokol, compiled from source into a game the way hologram is. It runs on D3D11 today; GLSL and Metal wait on hologram's tracers in those dialects learning caps.

the name

Gerridae are the water striders, which stand on a surface without breaking it. Also the working title of a Texas Hold'Em Lava Dome track, "Rendezvous at 44i boo", published by magmacrunch music.

hologram contact

hologram

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