278 lines
11 KiB
TypeScript
278 lines
11 KiB
TypeScript
import { Color } from "./Color"
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import type { Framebuffer } from "./Framebuffer"
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import type { Fog, RenderConfig } from "./RenderConfig"
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import { Texture } from "./Texture"
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import type { Mat4 } from "../math/Mat4"
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import { STRIDE, type Mesh } from "../scene/Mesh"
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/** Anything with w below this is treated as behind the camera and clipped. */
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const NEAR_W = 0.01
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/** Fixed world-space directional light (normalized components). */
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const LIGHT_LEN = Math.hypot(0.4, 1, 0.35)
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const LIGHT_X = 0.4 / LIGHT_LEN
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const LIGHT_Y = 1 / LIGHT_LEN
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const LIGHT_Z = 0.35 / LIGHT_LEN
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const AMBIENT = 0.4
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const DIFFUSE = 0.6
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/** Floats per clip-space vertex in the scratch buffers: x, y, w, u, v (clip z is
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* unused, so it is dropped). */
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const CLIP = 5
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/** Reused per-triangle scratch: the 3 projected verts (`src`) and the near-clip
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* result (`dst`, up to 4 verts). Module-level so the hot path never allocates.
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* Safe because a triangle is fully processed before the next one starts. */
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const src = new Float64Array(3 * CLIP)
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const dst = new Float64Array(4 * CLIP)
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/**
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* Software triangle rasterizer — the heart of the PS1 look.
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*
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* Per triangle the pipeline is: transform to clip space, clip against the near
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* plane, perspective-divide to screen pixels (optionally snapping vertices to a
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* grid), then fill with an edge-function / barycentric scan. Per pixel it
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* interpolates depth as 1/w, perspective-correct texture coords, and applies
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* flat shading plus distance fog.
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*
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* Meshes are stored flat (see `Mesh`) and the whole per-triangle path works in
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* reused scratch buffers, so drawing allocates nothing — no GC churn, no frame
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* spikes. `cull` enables backface culling for solid, consistently-wound meshes.
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*
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* The period-accurate rough edges are deliberate, not unfinished: no mipmaps
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* (so distant textures shimmer/moire) and no antialiasing (jagged silhouettes).
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*/
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export namespace Rasterizer {
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/** Draw an indexed mesh into the framebuffer through a view-projection matrix.
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* Shading is flat (one normal per face), computed once per triangle. `cull`
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* drops back-facing triangles (default off = double-sided). */
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export function draw(
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fb: Framebuffer,
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mesh: Mesh,
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texture: Texture,
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viewProj: Mat4,
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config: RenderConfig,
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cull = false,
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clipY0 = 0,
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clipY1 = 1 << 30,
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): void {
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const { verts, indices } = mesh
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const flat = config.lighting === "flat"
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for (let t = 0; t + 2 < indices.length; t += 3) {
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const o0 = indices[t] * STRIDE
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const o1 = indices[t + 1] * STRIDE
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const o2 = indices[t + 2] * STRIDE
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const shade = flat ? flatShade(verts, o0, o1, o2) : 1
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project(viewProj, verts, o0, 0)
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project(viewProj, verts, o1, CLIP)
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project(viewProj, verts, o2, CLIP * 2)
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// Near-clipping can turn one triangle into a quad; fan it back to tris.
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const n = clipNear(3)
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for (let k = 1; k + 1 < n; k++) {
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fillTriangle(fb, 0, k, k + 1, shade, texture, config, cull, clipY0, clipY1)
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}
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}
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}
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/** Transform vertex `o` of `verts` by `m` into clip space, written to `src` at
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* `out`. Only x, y, w are needed (z is unused); the matrix multiply is inlined
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* to avoid allocating a result object. */
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function project(m: Mat4, verts: number[], o: number, out: number): void {
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const x = verts[o]
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const y = verts[o + 1]
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const z = verts[o + 2]
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src[out] = m[0] * x + m[4] * y + m[8] * z + m[12]
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src[out + 1] = m[1] * x + m[5] * y + m[9] * z + m[13]
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src[out + 2] = m[3] * x + m[7] * y + m[11] * z + m[15]
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src[out + 3] = verts[o + 3]
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src[out + 4] = verts[o + 4]
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}
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/** Flat (per-face) directional shade in 0..1: ambient plus diffuse from the
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* face normal (cross of two edges). `abs()` makes it two-sided so back-facing
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* tris still light. Reads positions straight from the flat vertex array. */
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function flatShade(verts: number[], o0: number, o1: number, o2: number): number {
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const ax = verts[o0]
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const ay = verts[o0 + 1]
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const az = verts[o0 + 2]
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const e1x = verts[o1] - ax
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const e1y = verts[o1 + 1] - ay
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const e1z = verts[o1 + 2] - az
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const e2x = verts[o2] - ax
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const e2y = verts[o2 + 1] - ay
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const e2z = verts[o2 + 2] - az
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const nx = e1y * e2z - e1z * e2y
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const ny = e1z * e2x - e1x * e2z
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const nz = e1x * e2y - e1y * e2x
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const len = Math.hypot(nx, ny, nz)
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if (len === 0) {
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return AMBIENT
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}
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const d = Math.abs((nx * LIGHT_X + ny * LIGHT_Y + nz * LIGHT_Z) / len)
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return Math.min(1, AMBIENT + DIFFUSE * d)
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}
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/**
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* Clip the `count`-vertex polygon in `src` against the camera plane (w =
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* NEAR_W) with a single Sutherland-Hodgman pass, writing the result (0, 3, or
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* 4 verts) to `dst` and returning its vertex count.
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*
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* Geometry intersecting the camera plane has vertices both in front of and
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* behind the eye. Without clipping, the behind
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* vertices have w <= 0 and invert under the perspective divide, smearing the
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* triangle across the whole screen (and risking divide-by-zero).
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*/
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function clipNear(count: number): number {
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let out = 0
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for (let i = 0; i < count; i++) {
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const ci = i * CLIP
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const pi = ((i + count - 1) % count) * CLIP
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const curW = src[ci + 2]
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const prevW = src[pi + 2]
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const curIn = curW >= NEAR_W
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const prevIn = prevW >= NEAR_W
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// Crossing the plane emits the intersection point before the inside one.
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if (curIn !== prevIn) {
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const t = (NEAR_W - prevW) / (curW - prevW)
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const o = out * CLIP
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dst[o] = src[pi] + (src[ci] - src[pi]) * t
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dst[o + 1] = src[pi + 1] + (src[ci + 1] - src[pi + 1]) * t
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dst[o + 2] = prevW + (curW - prevW) * t
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dst[o + 3] = src[pi + 3] + (src[ci + 3] - src[pi + 3]) * t
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dst[o + 4] = src[pi + 4] + (src[ci + 4] - src[pi + 4]) * t
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out++
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}
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if (curIn) {
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const o = out * CLIP
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dst[o] = src[ci]
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dst[o + 1] = src[ci + 1]
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dst[o + 2] = curW
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dst[o + 3] = src[ci + 3]
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dst[o + 4] = src[ci + 4]
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out++
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}
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}
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return out
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}
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/**
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* Scan-convert one clip-space triangle (verts `ia`, `ib`, `ic` in `dst`).
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*
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* Vertex snap: real PS1 hardware transformed vertices in low-precision fixed
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* point, so screen positions popped between pixels as the camera moved (the
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* trademark "vertex wobble"). We emulate it by snapping to a `snap`-pixel grid.
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*/
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function fillTriangle(
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fb: Framebuffer,
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ia: number,
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ib: number,
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ic: number,
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shade: number,
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texture: Texture,
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config: RenderConfig,
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cull: boolean,
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clipY0: number,
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clipY1: number,
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): void {
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const oa = ia * CLIP
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const ob = ib * CLIP
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const oc = ic * CLIP
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const width = fb.width
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const height = fb.height
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const snap = config.vertexSnap
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const invWa = 1 / dst[oa + 2]
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const invWb = 1 / dst[ob + 2]
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const invWc = 1 / dst[oc + 2]
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let sxA = (dst[oa] * invWa * 0.5 + 0.5) * width
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let syA = (1 - (dst[oa + 1] * invWa * 0.5 + 0.5)) * height
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let sxB = (dst[ob] * invWb * 0.5 + 0.5) * width
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let syB = (1 - (dst[ob + 1] * invWb * 0.5 + 0.5)) * height
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let sxC = (dst[oc] * invWc * 0.5 + 0.5) * width
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let syC = (1 - (dst[oc + 1] * invWc * 0.5 + 0.5)) * height
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if (snap > 0) {
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sxA = Math.round(sxA / snap) * snap
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syA = Math.round(syA / snap) * snap
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sxB = Math.round(sxB / snap) * snap
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syB = Math.round(syB / snap) * snap
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sxC = Math.round(sxC / snap) * snap
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syC = Math.round(syC / snap) * snap
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}
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// Signed area x2; its sign is the screen winding.
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const area = (sxB - sxA) * (syC - syA) - (syB - syA) * (sxC - sxA)
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if (area === 0) {
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return
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}
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// Backface cull: a back-facing triangle has positive area here. Only for
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// solid, consistently-wound meshes; other materials may stay double-sided.
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if (cull && area > 0) {
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return
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}
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const invArea = 1 / area
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const uA = dst[oa + 3]
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const vA = dst[oa + 4]
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const uB = dst[ob + 3]
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const vB = dst[ob + 4]
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const uC = dst[oc + 3]
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const vC = dst[oc + 4]
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const minX = Math.max(0, Math.floor(Math.min(sxA, sxB, sxC)))
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const maxX = Math.min(width - 1, Math.ceil(Math.max(sxA, sxB, sxC)))
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// Clamp to the caller's Y-band (default full frame) so worker threads can
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// each fill a disjoint slice of rows without ever touching the same pixel.
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const minY = Math.max(0, clipY0, Math.floor(Math.min(syA, syB, syC)))
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const maxY = Math.min(height - 1, clipY1 - 1, Math.ceil(Math.max(syA, syB, syC)))
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// Edge deltas for the three barycentric edge functions (b->c, c->a, a->b).
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const dx0 = sxC - sxB
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const dy0 = syC - syB
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const dx1 = sxA - sxC
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const dy1 = syA - syC
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const dx2 = sxB - sxA
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const dy2 = syB - syA
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const fog = config.fog
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const filter = config.textureFilter
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const color = fb.color
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const depth = fb.depth
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for (let y = minY; y <= maxY; y++) {
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const py = y + 0.5
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const rowStart = y * width
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for (let x = minX; x <= maxX; x++) {
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const px = x + 0.5
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// Barycentric weights, normalized so they sum to 1. Dividing by a signed
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// area accepts either winding.
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const w0 = (dx0 * (py - syB) - dy0 * (px - sxB)) * invArea
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if (w0 < 0) {
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continue
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}
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const w1 = (dx1 * (py - syC) - dy1 * (px - sxC)) * invArea
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if (w1 < 0) {
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continue
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}
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const w2 = (dx2 * (py - syA) - dy2 * (px - sxA)) * invArea
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if (w2 < 0) {
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continue
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}
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// 1/w interpolates linearly in screen space. Larger = nearer.
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const invW = w0 * invWa + w1 * invWb + w2 * invWc
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const idx = rowStart + x
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if (invW <= depth[idx]) {
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continue
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}
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// Perspective-correct texture coords: divide interpolated u/w, v/w by 1/w
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// to undo foreshortening, so textures sit flat on receding surfaces.
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const u = (w0 * uA * invWa + w1 * uB * invWb + w2 * uC * invWc) / invW
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const v = (w0 * vA * invWa + w1 * vB * invWb + w2 * vC * invWc) / invW
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// Alpha cutout: discard transparent texels so sprites read as cutouts.
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const texel = Texture.sample(texture, u, v, filter)
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if (Color.a(texel) < 128) {
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continue
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}
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color[idx] = fog === null ? Color.scale(texel, shade) : shadeFog(texel, shade, fog, invW)
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depth[idx] = invW
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}
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}
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}
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/** Shade a texel then fade it toward the fog color by view-space distance. */
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function shadeFog(texel: Color, shade: number, fog: Fog, invW: number): Color {
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const dist = 1 / invW
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const f = Math.min(1, Math.max(0, (fog.far - dist) / (fog.far - fog.near)))
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return Color.lerp(fog.color, Color.scale(texel, shade), f)
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}
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}
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