42 lines
1.5 KiB
TypeScript
42 lines
1.5 KiB
TypeScript
import type { Vec2 } from "../math/Vec2"
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import type { Vec3 } from "../math/Vec3"
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import type { Texture } from "../render/Texture"
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import { Camera } from "./Camera"
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import type { Mesh } from "./Mesh"
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/** A flat image standing in the world, always turned to face the camera --
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* how the PS1 drew most enemies and props instead of 3D models. */
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export type Sprite = {
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/** World anchor at the base (feet) center. */
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position: Vec3
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/** World-space width and height. */
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size: Vec2
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texture: Texture
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}
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export namespace Sprite {
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/**
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* Build the sprite's quad as a Y-axis billboard: it spins around vertical to
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* face the camera but stays upright, so characters never tilt. Draw the
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* result with Rasterizer.draw (its alpha cutout hides transparent texels).
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*/
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export function billboard(sprite: Sprite, camera: Camera): Mesh {
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const forward = Camera.forward(camera)
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// Camera right projected onto the ground plane (== normalize(-fz, 0, fx)).
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const len = Math.hypot(forward.x, forward.z) || 1
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const rx = -forward.z / len
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const rz = forward.x / len
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const hw = sprite.size.x / 2
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const p = sprite.position
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const y0 = p.y
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const y1 = p.y + sprite.size.y
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const lx = p.x - rx * hw
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const lz = p.z - rz * hw
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const gx = p.x + rx * hw
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const gz = p.z + rz * hw
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// Flat verts (x, y, z, u, v) per corner: bottom-left, bottom-right, top-right,
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// top-left.
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const verts = [lx, y0, lz, 0, 1, gx, y0, gz, 1, 1, gx, y1, gz, 1, 0, lx, y1, lz, 0, 0]
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return { verts, indices: [0, 1, 2, 0, 2, 3] }
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}
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}
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