gameframe-d3d

Direct3D 3 immediate mode as games of 1997 drove it, in software. A game's Direct3D build writes transformed and lit vertices (D3DTLVERTEX) and an instruction stream into an execute buffer and hands it to IDirect3DDevice::Execute. A port that has traced what goes into those buffers can write the same buffers with Builder and run them with Device, at any multiple of the game's resolution, with no DirectX and no GPU, natively and in WebAssembly.

What it models:

• execute buffers: D3DOP_PROCESSVERTICES (COPY), D3DOP_STATERENDER and D3DOP_TRIANGLE, written by Builder and read by exec::parse, as the documentation's structures lay them out. Other opcodes are counted in Device::skipped;
• the render states by their D3DRENDERSTATETYPE numbers (consts::rs);
• the rasterisation rules: pixel centres at integer coordinates and the top-left filling convention, so triangles that share an edge draw each pixel once; culling by winding;
• flat shading (the first vertex's colour) and Gouraud shading; textures interpolated perspective-correct with TEXTUREPERSPECTIVE, everything else in screen space;
• textures in RGB565, ARGB1555 and ARGB4444, nearest or linear, wrapped, mirrored or clamped, and a surface's colour key on a card with D3DPTEXTURECAPS_TRANSPARENCY;
• the texture blends DECAL, MODULATE, DECALALPHA, MODULATEALPHA, COPY and ADD;
• the specular colour, vertex fog (the specular alpha as the fog factor, with FOGCOLOR), the alpha test, the stipple pattern, and blending with every D3DBLEND factor;
• the depth buffer with every D3DCMPFUNC, and an RGB565 target.

The rules come from Microsoft's public documentation of Direct3D immediate mode (the DirectX 3 and 5 SDK help, and the later pages "Rasterization Rules" and "Directly Mapping Texels to Pixels"), read as prose. No other implementation's source was read. Where the documentation leaves a detail open the code says so in a Deviation: comment: the stipple bit order, the stippled-alpha pattern, the defaults DirectX 3 does not list, no dither, no table fog, no mip levels. Nothing has been compared with a real card yet; real drivers differed from each other in these details.

use gameframe_d3d::{Builder, Device, TlVertex, consts::*};
let mut b = Builder::new();
let v = |sx, sy| TlVertex { sx, sy, sz: 0.5, rhw: 1.0, color: 0xffff_0000, ..TlVertex::default() };
let i = [b.vertex(v(0.0, 0.0)), b.vertex(v(8.0, 0.0)), b.vertex(v(0.0, 8.0))];
let n = b.vertex_count() as u32;
b.process_vertices(PROCESS_COPY, 0, 0, n);
b.render_states(&[(rs::CULLMODE, CULL_NONE)]);
b.triangle(i);
let (buf, data) = b.finish();
let mut d = Device::new(16, 16, 2.0);
d.execute(&buf, &data);
assert_eq!(d.colour[2 * 32 + 2], 0xf800);

Licence: Apache 2.0 (code), CC0 1.0 (this text).