Globe: Tile borders fix

src/geo/projection/globe.ts

@@ -23,14 +23,16 @@ export const globeConstants = {
 
 const granularitySettingsGlobe: SubdivisionGranularitySetting = new SubdivisionGranularitySetting({
     fill: new SubdivisionGranularityExpression(128, 1),
-    line: new SubdivisionGranularityExpression(512, 1),
+    line: new SubdivisionGranularityExpression(512, 0),
     // Always keep at least some subdivision on raster tiles, etc,
     // otherwise they will be visibly warped at high zooms (before mercator transition).
     // This si not needed on fill, because fill geometry tends to already be
     // highly tessellated and granular at high zooms.
-    // Minimal granularity of 8 seems to be enough to avoid warped raster tiles, while also minimizing triangle count.
     tile: new SubdivisionGranularityExpression(128, 32),
-    stencil: new SubdivisionGranularityExpression(128, 4),
+    // Stencil granularity must never be higher than fill granularity,
+    // otherwise we would get seams in the oceans at zoom levels where
+    // stencil has higher granularity than fill.
+    stencil: new SubdivisionGranularityExpression(128, 1),
     circle: 3
 });
 

src/render/draw_fill.ts

@@ -15,7 +15,6 @@ import type {FillStyleLayer} from '../style/style_layer/fill_style_layer';
 import type {FillBucket} from '../data/bucket/fill_bucket';
 import type {OverscaledTileID} from '../source/tile_id';
 import {updatePatternPositionsInProgram} from './update_pattern_positions_in_program';
-import {StencilMode} from '../gl/stencil_mode';
 import {translatePosition} from '../util/util';
 
 export function drawFill(painter: Painter, sourceCache: SourceCache, layer: FillStyleLayer, coords: Array<OverscaledTileID>) {
@@ -124,27 +123,7 @@ function drawFillTiles(
                 fillOutlineUniformValues(drawingBufferSize, translateForUniforms);
         }
 
-        // Stencil is not really needed for anything unless we are drawing transparent things.
-        //
-        // For translucent layers, we must draw any pixel of a given layer at most once,
-        // otherwise we might get artifacts from the transparent geometry being drawn twice over itself,
-        // which can happen due to tiles having a slight overlapping border into neighboring tiles.
-        // Hence we use stencil tile masks for any translucent pass, including for fill.
-        //
-        // Globe rendering relies on these tile borders to hide tile seams, since under globe projection
-        // tiles are not squares, but slightly curved squares. At high zoom levels, the tile stencil mask
-        // is approximated by a square, but if the tile contains fine geometry, it might still get projected
-        // into a curved shape, causing a mismatch with the stencil mask, which is very visible
-        // if the tile border is small.
-        //
-        // The simples workaround for this is to just disable stencil masking for opaque fill layers,
-        // since the fine geometry will always line up perfectly with the geometry in its neighboring tiles,
-        // even if the border is small. Disabling stencil ensures the neighboring geometry isn't clipped.
-        //
-        // This doesn't seem to be an issue for transparent fill layers (or they don't get used enough to be noticeable),
-        // which is a good thing, since there is no easy solution for this problem for transparency, other than
-        // greatly increasing subdivision granularity for both fill layers and stencil masks, at least at tile edges.
-        const stencil = (painter.renderPass === 'translucent') ? painter.stencilModeForClipping(coord) : StencilMode.disabled;
+        const stencil = painter.stencilModeForClipping(coord);
 
         program.draw(painter.context, drawMode, depthMode,
             stencil, colorMode, CullFaceMode.backCCW, uniformValues, terrainData, projectionData,

src/shaders/_projection_globe.vertex.glsl

@@ -44,7 +44,7 @@ float projectLineThickness(float tileY) {
 }
 
 // get position inside the tile in range 0..8192 and project it onto the surface of a unit sphere
-vec3 projectToSphere(vec2 posInTile) {
+vec3 projectToSphere(vec2 posInTile, vec2 rawPos) {
     // Compute position in range 0..1 of the base tile of web mercator
     vec2 mercator_pos = u_projection_tile_mercator_coords.xy + u_projection_tile_mercator_coords.zw * posInTile;
 
@@ -61,17 +61,21 @@ vec3 projectToSphere(vec2 posInTile) {
     );
 
     // North pole
-    if (posInTile.y < -32767.5) {
+    if (rawPos.y < -32767.5) {
         pos = vec3(0.0, 1.0, 0.0);
     }
     // South pole
-    if (posInTile.y > 32766.5) {
+    if (rawPos.y > 32766.5) {
         pos = vec3(0.0, -1.0, 0.0);
     }
 
     return pos;
 }
 
+vec3 projectToSphere(vec2 posInTile) {
+    return projectToSphere(posInTile, vec2(0.0, 0.0));
+}
+
 float globeComputeClippingZ(vec3 spherePos) {
     return (1.0 - (dot(spherePos, u_projection_clipping_plane.xyz) + u_projection_clipping_plane.w));
 }
@@ -117,6 +121,11 @@ vec4 projectTile(vec2 posInTile) {
     return interpolateProjection(posInTile, projectToSphere(posInTile), 0.0);
 }
 
+// A variant that supports special pole and planet center vertices.
+vec4 projectTile(vec2 posInTile, vec2 rawPos) {
+    return interpolateProjection(posInTile, projectToSphere(posInTile, rawPos), 0.0);
+}
+
 // Uses elevation to compute final screenspace projection
 // and **replaces Z** with a custom value that clips geometry
 // on the backfacing side of the planet.

src/shaders/_projection_mercator.vertex.glsl

@@ -8,10 +8,16 @@ float projectCircleRadius(float tileY) {
 
 // Projects a point in tile-local coordinates (usually 0..EXTENT) to screen.
 vec4 projectTile(vec2 p) {
+    vec4 result = u_projection_matrix * vec4(p, 0.0, 1.0);
+    return result;
+}
+
+// Projects a point in tile-local coordinates (usually 0..EXTENT) to screen, and handle special pole or planet center vertices.
+vec4 projectTile(vec2 p, vec2 rawPos) {
     // Kill pole vertices and triangles by placing the pole vertex so far in Z that
     // the clipping hardware kills the entire triangle.
     vec4 result = u_projection_matrix * vec4(p, 0.0, 1.0);
-    if (p.y < -32767.5 || p.y > 32766.5) {
+    if (rawPos.y < -32767.5 || rawPos.y > 32766.5) {
         result.z = -10000000.0;
     }
     return result;

src/shaders/fill.vertex.glsl

@@ -9,5 +9,5 @@ void main() {
     #pragma mapbox: initialize highp vec4 color
     #pragma mapbox: initialize lowp float opacity
 
-    gl_Position = projectTile(a_pos + u_fill_translate);
+    gl_Position = projectTile(a_pos + u_fill_translate, a_pos);
 }

src/shaders/fill_extrusion.vertex.glsl

@@ -53,7 +53,7 @@ void main() {
     vec2 posInTile = a_pos + u_fill_translate;
 
     #ifdef GLOBE
-        vec3 spherePos = projectToSphere(posInTile);
+        vec3 spherePos = projectToSphere(posInTile, a_pos);
         vec3 elevatedPos = spherePos * (1.0 + elevation / GLOBE_RADIUS);
         v_sphere_pos = elevatedPos;
         gl_Position = interpolateProjectionFor3D(posInTile, spherePos, elevation);

src/shaders/fill_extrusion_pattern.vertex.glsl

@@ -77,7 +77,7 @@ void main() {
     vec2 posInTile = a_pos + u_fill_translate;
 
     #ifdef GLOBE
-        vec3 spherePos = projectToSphere(posInTile);
+        vec3 spherePos = projectToSphere(posInTile, a_pos);
         vec3 elevatedPos = spherePos * (1.0 + elevation / GLOBE_RADIUS);
         v_sphere_pos = elevatedPos;
         gl_Position = interpolateProjectionFor3D(posInTile, spherePos, elevation);

src/shaders/fill_outline.vertex.glsl

@@ -15,7 +15,7 @@ void main() {
     #pragma mapbox: initialize highp vec4 outline_color
     #pragma mapbox: initialize lowp float opacity
 
-    gl_Position = projectTile(a_pos + u_fill_translate);
+    gl_Position = projectTile(a_pos + u_fill_translate, a_pos);
 
     v_pos = (gl_Position.xy / gl_Position.w + 1.0) / 2.0 * u_world;
     #ifdef GLOBE

src/shaders/fill_outline_pattern.vertex.glsl

@@ -35,7 +35,7 @@ void main() {
     float fromScale = u_scale.y;
     float toScale = u_scale.z;
 
-    gl_Position = projectTile(a_pos + u_fill_translate);
+    gl_Position = projectTile(a_pos + u_fill_translate, a_pos);
 
     vec2 display_size_a = (pattern_br_a - pattern_tl_a) / pixel_ratio_from;
     vec2 display_size_b = (pattern_br_b - pattern_tl_b) / pixel_ratio_to;

src/shaders/fill_pattern.vertex.glsl

@@ -33,7 +33,7 @@ void main() {
     vec2 display_size_a = (pattern_br_a - pattern_tl_a) / pixel_ratio_from;
     vec2 display_size_b = (pattern_br_b - pattern_tl_b) / pixel_ratio_to;
 
-    gl_Position = projectTile(a_pos + u_fill_translate);
+    gl_Position = projectTile(a_pos + u_fill_translate, a_pos);
 
     v_pos_a = get_pattern_pos(u_pixel_coord_upper, u_pixel_coord_lower, fromScale * display_size_a, tileZoomRatio, a_pos);
     v_pos_b = get_pattern_pos(u_pixel_coord_upper, u_pixel_coord_lower, toScale * display_size_b, tileZoomRatio, a_pos);

src/shaders/hillshade.vertex.glsl

@@ -5,7 +5,7 @@ in vec2 a_pos;
 out vec2 v_pos;
 
 void main() {
-    gl_Position = projectTile(a_pos);
+    gl_Position = projectTile(a_pos, a_pos);
     v_pos = a_pos / 8192.0;
     // North pole
     if (a_pos.y < -32767.5) {

src/shaders/raster.vertex.glsl

@@ -14,14 +14,14 @@ void main() {
     // Interpolate the actual desired coordinates to get the final position.
     vec2 fractionalPos = a_pos / 8192.0;
     vec2 position = mix(mix(u_coords_top.xy, u_coords_top.zw, fractionalPos.x), mix(u_coords_bottom.xy, u_coords_bottom.zw, fractionalPos.x), fractionalPos.y);
-    gl_Position = projectTile(position);
+    gl_Position = projectTile(position, position);
 
     // We are using Int16 for texture position coordinates to give us enough precision for
     // fractional coordinates. We use 8192 to scale the texture coordinates in the buffer
     // as an arbitrarily high number to preserve adequate precision when rendering.
     // This is also the same value as the EXTENT we are using for our tile buffer pos coordinates,
     // so math for modifying either is consistent.
-    v_pos0 = ((fractionalPos - 0.5) / u_buffer_scale ) + 0.5;
+    v_pos0 = ((fractionalPos - 0.5) / u_buffer_scale) + 0.5;
 
      // When globe rendering is enabled, pole vertices need special handling to get nice texture coordinates.
     #ifdef GLOBE

test/integration/render/tests/fill-outside-tile/style.json

@@ -0,0 +1,37 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "description": "Tests that tiles are properly clipped by drawing a tile that has all its geometry outside its visible area. See issue #4803. The expected (correct) result is that nothing is drawn.",
+      "width": 64,
+      "height": 64
+    }
+  },
+  "zoom": 2.125,
+  "sources": {
+    "vector_tiles": {
+      "type": "vector",
+      "tiles": [
+        "local://tiles/outside_ring.mvt"
+      ]
+    }
+  },
+  "layers": [
+    {
+      "id": "background",
+      "type": "background",
+      "paint": {
+        "background-color": "white"
+      }
+    },
+    {
+      "id": "ocean",
+      "type": "fill",
+      "source": "vector_tiles",
+      "source-layer": "water",
+      "paint": {
+        "fill-color": "black"
+      }
+    }
+  ]
+}