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fix: correct coordinate rendering offset at maximum zoom via fp64 viewport center #2817

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fix: correct coordinate rendering offset at maximum zoom via fp64 viewport center #2817

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Initial plan
Copilot Feb 25, 2026
338a416
fix: add u_ViewportCenterLow uniform to fix coordinate precision at m…
Copilot Feb 25, 2026
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25 changes: 20 additions & 5 deletions packages/core/src/services/coordinate/CoordinateSystemService.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -26,15 +26,16 @@ export default class CoordinateSystemService implements ICoordinateSystemService
private viewportCenter: [number, number];

/**
* 屏幕中心点的最终投影结果，在 CPU 侧计算后传入 Shader
* @see https://zhuanlan.zhihu.com/p/57469121
* 屏幕中心点的 fp64 低精度部分，用于高精度坐标偏移计算
* fp64LowPart(x) = x - Math.fround(x)
*/
private viewportCenterProjection: [number, number, number, number];
private viewportCenterLow: [number, number] = [0, 0];

/**
* 像素单位 -> 经纬度 [x, y, z]
* 屏幕中心点的最终投影结果，在 CPU 侧计算后传入 Shader
* @see https://zhuanlan.zhihu.com/p/57469121
*/
private pixelsPerDegree: [number, number, number];
private viewportCenterProjection: [number, number, number, number];

/**
* 像素单位 -> 经纬度 [lng, lat] 使用泰勒级数展开
Expand All @@ -48,6 +49,11 @@ export default class CoordinateSystemService implements ICoordinateSystemService
*/
private pixelsPerMeter: [number, number, number];

/**
* 像素单位 -> 经纬度 [x, y, z]
*/
private pixelsPerDegree: [number, number, number];

/**
* 重新计算当前坐标系参数
* TODO: 使用 memoize 缓存参数以及计算结果
Expand All @@ -66,6 +72,11 @@ export default class CoordinateSystemService implements ICoordinateSystemService
zoom,
});
this.viewportCenter = center;
// 计算 fp64 低精度部分，用于高精度坐标偏移：fp64LowPart(x) = x - Math.fround(x)
this.viewportCenterLow = [
center[0] - Math.fround(center[0]),
center[1] - Math.fround(center[1]),
];
this.viewportCenterProjection = [0, 0, 0, 0];
this.pixelsPerMeter = pixelsPerMeter;
this.pixelsPerDegree = pixelsPerDegree;
Expand Down Expand Up @@ -102,6 +113,10 @@ export default class CoordinateSystemService implements ICoordinateSystemService
return this.viewportCenterProjection;
}

public getViewportCenterLow(): [number, number] {
return this.viewportCenterLow;
}

public getPixelsPerDegree(): [number, number, number] {
return this.pixelsPerDegree;
}
Expand Down
2 changes: 2 additions & 0 deletions packages/core/src/services/coordinate/ICoordinateSystemService.ts
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Expand Up @@ -21,6 +21,7 @@ export const CoordinateUniform = {
CoordinateSystem: 'u_CoordinateSystem',
ViewportCenter: 'u_ViewportCenter',
ViewportCenterProjection: 'u_ViewportCenterProjection',
ViewportCenterLow: 'u_ViewportCenterLow',
PixelsPerDegree: 'u_PixelsPerDegree',
PixelsPerDegree2: 'u_PixelsPerDegree2',
PixelsPerMeter: 'u_PixelsPerMeter',
Expand All @@ -35,6 +36,7 @@ export interface ICoordinateSystemService {
getViewportCenter(): [number, number];
setViewportCenter(center: [number, number]): void;
getViewportCenterProjection(): [number, number, number, number];
getViewportCenterLow(): [number, number];
getPixelsPerDegree(): [number, number, number];
getPixelsPerDegree2(): [number, number, number];
getPixelsPerMeter(): [number, number, number];
Expand Down
5 changes: 3 additions & 2 deletions packages/core/src/shaders/projection.glsl
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Expand Up @@ -84,10 +84,11 @@ vec4 project_position(vec4 position, vec2 position64xyLow) {
vec2 center = u_ViewportCenter;
float X = absolutePosition.x - center.x;
float Y = absolutePosition.y - center.y;
// 减去中心点的低精度部分，实现全双精度坐标计算，解决高缩放级别下坐标偏移问题
return project_offset(
vec4(
X + absolutePosition64xyLow.x,
Y + absolutePosition64xyLow.y,
X + absolutePosition64xyLow.x - u_ViewportCenterLow.x,
Y + absolutePosition64xyLow.y - u_ViewportCenterLow.y,
absolutePosition.z,
absolutePosition.w
)
Expand Down
1 change: 1 addition & 0 deletions packages/core/src/shaders/scene_uniforms.glsl
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Expand Up @@ -17,4 +17,5 @@ layout(std140) uniform SceneUniforms {
float u_FocalDistance;
vec2 u_RelativeOrigin;
float u_Reserved3;
vec2 u_ViewportCenterLow;
};
5 changes: 4 additions & 1 deletion packages/layers/src/plugins/ShaderUniformPlugin.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -118,6 +118,7 @@ export default class ShaderUniformPlugin implements ILayerPlugin {
const u_ViewportSize = [width, height];
const u_FocalDistance = this.cameraService.getFocalDistance();
const u_RelativeOrigin = offset && offset.length >= 2 ? [offset[0], offset[1]] : [0, 0];
const u_ViewportCenterLow = this.coordinateSystemService.getViewportCenterLow();

const data: number[] = [
...u_ViewMatrix, // 16
Expand All @@ -137,7 +138,8 @@ export default class ShaderUniformPlugin implements ILayerPlugin {
...u_ViewportSize, // 4
u_FocalDistance, // 1
...u_RelativeOrigin, // 2
0, // padding
0, // padding (u_Reserved3)
...u_ViewportCenterLow, // 2
];

return {
Expand All @@ -155,6 +157,7 @@ export default class ShaderUniformPlugin implements ILayerPlugin {
[CoordinateUniform.CoordinateSystem]: u_CoordinateSystem,
[CoordinateUniform.ViewportCenter]: u_ViewportCenter,
[CoordinateUniform.ViewportCenterProjection]: u_ViewportCenterProjection,
[CoordinateUniform.ViewportCenterLow]: u_ViewportCenterLow,
[CoordinateUniform.PixelsPerDegree]: u_PixelsPerDegree,
[CoordinateUniform.PixelsPerDegree2]: u_PixelsPerDegree2,
[CoordinateUniform.PixelsPerMeter]: u_PixelsPerMeter,
Expand Down
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