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feat: terrain

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This commit is contained in:
Dan Finch 2026-08-04 12:51:07 +02:00
parent f86b4ada13
commit 81474b6bca
13 changed files with 251 additions and 279 deletions
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33
engine/render/Rasterizer.ts
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@ -28,14 +28,13 @@ const DIFFUSE = 0.6
* Per triangle the pipeline is: transform to clip space, clip against the near
* plane, perspective-divide to screen pixels (optionally snapping vertices to a
* grid), then fill with an edge-function / barycentric scan. Per pixel it
* interpolates depth as 1/w, texture coords (affine or perspective-correct, see
* `fillTriangle`), and applies flat shading plus distance fog.
* interpolates depth as 1/w, perspective-correct texture coords, and applies
* flat shading plus distance fog.
*
* The period-accurate rough edges are deliberate, not unfinished: no mipmaps
* (so distant textures shimmer/moire), no antialiasing (jagged silhouettes),
* and affine texturing by default (the texture "swim"). Depth is a plain 1/w
* z-buffer and triangles are drawn double-sided (no backface culling), so mesh
* winding can never cause surfaces to drop out.
* (so distant textures shimmer/moire) and no antialiasing (jagged silhouettes).
* Depth is a plain 1/w z-buffer and triangles are drawn double-sided (no
* backface culling), so mesh winding can never cause surfaces to drop out.
*/
export namespace Rasterizer {
/** Draw an indexed mesh into the framebuffer through a view-projection
@ -159,7 +158,6 @@ export namespace Rasterizer {
const maxX = Math.min(fb.width - 1, Math.ceil(Math.max(a.sx, b.sx, c.sx)))
const minY = Math.max(0, Math.floor(Math.min(a.sy, b.sy, c.sy)))
const maxY = Math.min(fb.height - 1, Math.ceil(Math.max(a.sy, b.sy, c.sy)))
const pc = config.perspectiveCorrect
const fog = config.fog
for (let y = minY; y <= maxY; y++) {
for (let x = minX; x <= maxX; x++) {
@ -180,22 +178,11 @@ export namespace Rasterizer {
if (invW <= fb.depth[idx]) {
continue
}
// Two ways to interpolate texture coords across the triangle:
// affine - linear in screen space. This is what hardware without a
// perspective divide does. It is exact ONLY when the three vertices
// share a depth (a face viewed head-on). On a receding surface (the
// floor, or a wall turned into the periphery) the depth gradient
// makes it diverge, bending the texture along the triangle diagonal
// -- the signature PS1 "texture swim".
// persp - divide the interpolated u/w by the interpolated 1/w to
// undo foreshortening. Geometrically correct, no swim.
// perspectiveCorrect (0..1) lerps between them, so the look is a dial.
const uAff = w0 * a.u + w1 * b.u + w2 * c.u
const vAff = w0 * a.v + w1 * b.v + w2 * c.v
const uPer = (w0 * a.u * a.invW + w1 * b.u * b.invW + w2 * c.u * c.invW) / invW
const vPer = (w0 * a.v * a.invW + w1 * b.v * b.invW + w2 * c.v * c.invW) / invW
const u = uAff + (uPer - uAff) * pc
const v = vAff + (vPer - vAff) * pc
// Perspective-correct texture coords: divide the interpolated u/w and
// v/w by the interpolated 1/w to undo foreshortening, so textures sit
// flat on receding surfaces with no affine "swim".
const u = (w0 * a.u * a.invW + w1 * b.u * b.invW + w2 * c.u * c.invW) / invW
const v = (w0 * a.v * a.invW + w1 * b.v * b.invW + w2 * c.v * c.invW) / invW
// Alpha cutout: discard transparent texels so sprites read as cutouts,
// not rectangles. Opaque world textures are alpha 255, so unaffected.
const texel = Texture.sample(texture, u, v, config.textureFilter)