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fix(textureatlas): Allocate texture space more incrementally on resize #13042

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fix(textureatlas): Allocate texture space more incrementally on resize #13042

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1 change: 1 addition & 0 deletions CHANGES.md
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@
- Billboards using `imageSubRegion` now render as expected. [#12585](https://github.com/CesiumGS/cesium/issues/12585)
- Improved scaling of SVGs in billboards [#13020](https://github.com/CesiumGS/cesium/issues/13020)
- Fixed unexpected outline artifacts around billboards [#13038](https://github.com/CesiumGS/cesium/issues/13038)
- Fixed image alignment in large billboard collections [#13042](https://github.com/CesiumGS/cesium/issues/13042)

#### Additions :tada:

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25 changes: 8 additions & 17 deletions packages/engine/Source/Renderer/TextureAtlas.js
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Expand Up @@ -364,26 +364,17 @@ TextureAtlas.prototype._resize = function (context, queueOffset = 0) {
toPack.push(queue[i]);
}

// At minimum, the texture will need to scale to accommodate the largest width and height
width = Math.max(maxWidth, width);
height = Math.max(maxHeight, height);
// At minimum, atlas must fit its largest input images. Texture coordinates are
// compressed to 0–1 with 12-bit precision, so use power-of-two size to align pixels.
width = CesiumMath.nextPowerOfTwo(Math.max(maxWidth, width));
height = CesiumMath.nextPowerOfTwo(Math.max(maxHeight, height));

if (!context.webgl2) {
width = CesiumMath.nextPowerOfTwo(width);
height = CesiumMath.nextPowerOfTwo(height);
}

// Determine by what factor the texture need to be scaled by at minimum
const areaDifference = areaQueued;
let scalingFactor = 1.0;
while (areaDifference / width / height >= 1.0) {
scalingFactor *= 2.0;
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@donmccurdy donmccurdy Nov 21, 2025

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Since we'll have ... er, other challenges ... if the texture atlas size exceeds 16K x 16K, in practice this loop can't spend more than 28 iterations for the largest supportable atlas size. No need to use a sliding scale factor (which may cause us to miss more optimal atlas sizes) to save a small number of iterations.


// Resize by one dimension
// Iteratively double the smallest dimension until atlas area is (approximately) sufficient.
while (areaQueued >= width * height) {
if (width > height) {
height *= scalingFactor;
height *= 2;
} else {
width *= scalingFactor;
width *= 2;
}
}

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116 changes: 70 additions & 46 deletions packages/engine/Specs/Renderer/TextureAtlasSpec.js
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Expand Up @@ -704,56 +704,16 @@ describe("Scene/TextureAtlas", function () {
expect(index2).toEqual(2);
expect(index3).toEqual(3);

// Webgl1 textures should only be powers of 2
const isWebGL2 = scene.frameState.context.webgl2;
const textureWidth = isWebGL2 ? 20 : 32;
const textureHeight = isWebGL2 ? 32 : 16;
const textureWidth = 32;
const textureHeight = 16;

const texture = atlas.texture;
expect(texture.pixelFormat).toEqual(PixelFormat.RGBA);
expect(texture.width).toEqual(textureWidth);
expect(texture.height).toEqual(textureHeight);

if (isWebGL2) {
expect(drawAtlas(atlas, [index0, index1, index2, index3])).toBe(
`
....................
....................
....................
....................
....................
....................
2222222222..........
2222222222..........
2222222222..........
2222222222..........
2222222222..........
2222222222..........
2222222222..........
2222222222..........
2222222222..........
2222222222..........
3333333333333333....
3333333333333333....
3333333333333333....
3333333333333333....
3333333333333333....
3333333333333333....
3333333333333333....
3333333333333333....
3333333333333333....
3333333333333333....
3333333333333333....
3333333333333333....
33333333333333330...
33333333333333330...
33333333333333330...
333333333333333301..
`.trim(),
);
} else {
expect(drawAtlas(atlas, [index0, index1, index2, index3])).toBe(
`
expect(drawAtlas(atlas, [index0, index1, index2, index3])).toBe(
`
3333333333333333................
3333333333333333................
3333333333333333................
Expand All @@ -771,8 +731,7 @@ describe("Scene/TextureAtlas", function () {
333333333333333322222222220.....
3333333333333333222222222201....
`.trim(),
);
}
);

let textureCoordinates = atlas.computeTextureCoordinates(index0);
expect(
Expand Down Expand Up @@ -1456,6 +1415,71 @@ describe("Scene/TextureAtlas", function () {
expect(guid1).not.toEqual(guid2);
});

it("allocates appropriate space on resize", async function () {
const imageWidth = 128;
const imageHeight = 64;

await addImages(25);
let inputPixels = 25 * imageWidth * imageHeight;
let atlasWidth = atlas.texture.width;
let atlasHeight = atlas.texture.height;

// Allocate enough space, but not >>2x more. Aspect ratio should be 1:1, 1:2, or 2:1.
expect(atlasWidth * atlasHeight).toBeGreaterThan(inputPixels);
expect(atlasWidth * atlasHeight).toBeLessThanOrEqual(inputPixels * 3);
expect(atlasWidth / atlasHeight).toBeGreaterThanOrEqual(0.5);
expect(atlasWidth / atlasHeight).toBeLessThanOrEqual(2.0);

await addImages(75);
inputPixels = 75 * imageWidth * imageHeight;
atlasWidth = atlas.texture.width;
atlasHeight = atlas.texture.height;

expect(atlasWidth * atlasHeight).toBeGreaterThan(inputPixels);
expect(atlasWidth * atlasHeight).toBeLessThanOrEqual(inputPixels * 3);
expect(atlasWidth / atlasHeight).toBeGreaterThanOrEqual(0.5);
expect(atlasWidth / atlasHeight).toBeLessThanOrEqual(2.0);

await addImages(256);
inputPixels = 256 * imageWidth * imageHeight;
atlasWidth = atlas.texture.width;
atlasHeight = atlas.texture.height;

expect(atlasWidth * atlasHeight).toBeGreaterThan(inputPixels);
expect(atlasWidth * atlasHeight).toBeLessThanOrEqual(inputPixels * 3);
expect(atlasWidth / atlasHeight).toBeGreaterThanOrEqual(0.5);
expect(atlasWidth / atlasHeight).toBeLessThanOrEqual(2.0);

async function addImages(count) {
atlas = new TextureAtlas();

const imageUrl = createImageDataURL(imageWidth, imageHeight);

const promises = [];
for (let i = 0; i < count; i++) {
promises.push(atlas.addImage(i.toString(), imageUrl));
}

await pollWhilePromise(Promise.all(promises), () => {
atlas.update(scene.frameState.context);
});

return count * imageWidth * imageHeight;
}

function createImageDataURL(width, height) {
const canvas = document.createElement("canvas");
canvas.width = width;
canvas.height = height;

const ctx = canvas.getContext("2d");
ctx.fillStyle = "green";
ctx.fillRect(0, 0, width, height);

return canvas.toDataURL();
}
});

it("destroys successfully while image is queued", async function () {
atlas = new TextureAtlas();

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