Method _applyFrame

packages/melonjs/src/renderable/sprite3d.js:534–631

* Apply the current frame's texture region to the quad — the geometry hook * called by the shared FrameAnimation engine (the 3D counterpart of * Sprite's sub-texture / size / anchor swap). Rewrites both the quad's * UVs (the atlas sub-rect, with a 90° corner permutation for pac

(region)

	 * @ignore
	 */
	_applyFrame(region) {
		// remember the region so a later flipX/flipY can re-map immediately
		this._region = region;
		// the texture backing this frame (full sheet for a spritesheet, the atlas
		// page for a packed atlas)
		const image = this.source.getTexture(region);
		const iw = image.width;
		const ih = image.height;

		// `region.width`/`height` are the art's UNROTATED dimensions; a
		// packer-rotated region occupies a height×width box in the atlas.
		const rotated = region.angle !== 0;
		const aw = region.width;
		const ah = region.height;
		const atlasW = rotated ? ah : aw;
		const atlasH = rotated ? aw : ah;

		// ── UVs: the atlas AABB, corners permuted 90° when the region is rotated
		const ox = region.offset.x;
		const oy = region.offset.y;
		const uL = ox / iw;
		const uR = (ox + atlasW) / iw;
		// texture-space top is the smaller pixel y; the baked UVs put v=0 at the
		// top corners (local +y) so the frame lands upright under Y-down.
		const vT = oy / ih;
		const vB = (oy + atlasH) / ih;
		const uv = this.uvs;
		// corners: 0=(left,bottom) 1=(right,bottom) 2=(right,top) 3=(left,top)
		if (rotated) {
			// TexturePacker stores rotated art 90° clockwise, so undo it by
			// rotating the corner→UV assignment: the quad's left edge samples the
			// atlas top row, its top edge samples the atlas right column.
			uv[0] = uL;
			uv[1] = vT; // BL → atlas top-left
			uv[2] = uL;
			uv[3] = vB; // BR → atlas bottom-left
			uv[4] = uR;
			uv[5] = vB; // TR → atlas bottom-right
			uv[6] = uR;
			uv[7] = vT; // TL → atlas top-right
		} else {
			uv[0] = uL;
			uv[1] = vB;
			uv[2] = uR;
			uv[3] = vB;
			uv[4] = uR;
			uv[5] = vT;
			uv[6] = uL;
			uv[7] = vT;
		}

		// ── geometry: place the (possibly trimmed) art rect inside the logical
		// frame. Logical size is the untrimmed sourceSize; the art occupies a
		// sub-rect offset by `trim`. The world quad (±_halfW/±_halfH) maps the
		// logical frame captured from the first applied frame, so trimmed frames
		// keep their position/size relative to the full sprite footprint.
		const trimmed = region.trimmed === true && region.sourceSize != null;
		const logicalW = trimmed ? region.sourceSize.w : aw;