ENH: Removes elevation max zoom from exaggeration calculation for raster-dem sources

debug/hillshade.html

@@ -21,7 +21,7 @@
         top: 10px;
         right: 10px;
         border-radius: 3px;
-        width: 120px;
+        width: 140px;
         border: 1px solid rgba(0,0,0,0.4);
         font-family: 'Open Sans', sans-serif;
     }
@@ -76,7 +76,7 @@
     map.addSource('mapbox-dem', {
         "type": "raster-dem",
         "url": "mapbox://mapbox.terrain-rgb",
-        "tileSize": 256
+        "tileSize": 256,
     });
     map.addLayer({
         "id": "Mapbox data",
@@ -106,9 +106,25 @@
     // where hillshading sits in the Mapbox Outdoors style
     }, 'waterway-river-canal-shadow');
 
+    // Add variant of Hillshade that overzooms beyond zoom 7.
+    // Note: source tiles are 512, so the following only goes up to native zoom 7.
+    map.addSource('mapbox-dem-z8', {
+        "type": "raster-dem",
+        "url": "mapbox://mapbox.terrain-rgb",
+        "tileSize": 256,
+        "maxzoom": 8
+    });
+    map.addLayer({
+        "id": "Mapbox data to Z8",
+        "source": "mapbox-dem-z8",
+        "type": "hillshade",
+        "layout": {
+            "visibility": "none"
+        }
+    }, 'waterway-river-canal-shadow');
 });
 
-var toggleableLayerIds = ['Mapbox data', 'Terrarium data'];
+var toggleableLayerIds = ['Mapbox data', 'Terrarium data', 'Mapbox data to Z8'];
 
 for (var i = 0; i < toggleableLayerIds.length; i++) {
     var id = toggleableLayerIds[i];

src/render/draw_hillshade.js

@@ -20,7 +20,6 @@ function drawHillshade(painter: Painter, sourceCache: SourceCache, layer: Hillsh
     if (painter.renderPass !== 'offscreen' && painter.renderPass !== 'translucent') return;
 
     const context = painter.context;
-    const sourceMaxZoom = sourceCache.getSource().maxzoom;
 
     const depthMode = painter.depthModeForSublayer(0, DepthMode.ReadOnly);
     const colorMode = painter.colorModeForRenderPass();
@@ -31,7 +30,7 @@ function drawHillshade(painter: Painter, sourceCache: SourceCache, layer: Hillsh
     for (const coord of coords) {
         const tile = sourceCache.getTile(coord);
         if (tile.needsHillshadePrepare && painter.renderPass === 'offscreen') {
-            prepareHillshade(painter, tile, layer, sourceMaxZoom, depthMode, StencilMode.disabled, colorMode);
+            prepareHillshade(painter, tile, layer, depthMode, StencilMode.disabled, colorMode);
         } else if (painter.renderPass === 'translucent') {
             renderHillshade(painter, tile, layer, depthMode, stencilModes[coord.overscaledZ], colorMode);
         }
@@ -60,7 +59,7 @@ function renderHillshade(painter, tile, layer, depthMode, stencilMode, colorMode
 
 // hillshade rendering is done in two steps. the prepare step first calculates the slope of the terrain in the x and y
 // directions for each pixel, and saves those values to a framebuffer texture in the r and g channels.
-function prepareHillshade(painter, tile, layer, sourceMaxZoom, depthMode, stencilMode, colorMode) {
+function prepareHillshade(painter, tile, layer, depthMode, stencilMode, colorMode) {
     const context = painter.context;
     const gl = context.gl;
     const dem = tile.dem;
@@ -99,7 +98,7 @@ function prepareHillshade(painter, tile, layer, sourceMaxZoom, depthMode, stenci
 
         painter.useProgram('hillshadePrepare').draw(context, gl.TRIANGLES,
             depthMode, stencilMode, colorMode, CullFaceMode.disabled,
-            hillshadeUniformPrepareValues(tile.tileID, dem, sourceMaxZoom),
+            hillshadeUniformPrepareValues(tile.tileID, dem),
             layer.id, painter.rasterBoundsBuffer,
             painter.quadTriangleIndexBuffer, painter.rasterBoundsSegments);
 

src/render/program/hillshade_program.js

@@ -36,7 +36,6 @@ export type HillshadePrepareUniformsType = {|
     'u_image': Uniform1i,
     'u_dimension': Uniform2f,
     'u_zoom': Uniform1f,
-    'u_maxzoom': Uniform1f,
     'u_unpack': Uniform4f
 |};
 
@@ -55,7 +54,6 @@ const hillshadePrepareUniforms = (context: Context, locations: UniformLocations)
     'u_image': new Uniform1i(context, locations.u_image),
     'u_dimension': new Uniform2f(context, locations.u_dimension),
     'u_zoom': new Uniform1f(context, locations.u_zoom),
-    'u_maxzoom': new Uniform1f(context, locations.u_maxzoom),
     'u_unpack': new Uniform4f(context, locations.u_unpack)
 });
 
@@ -86,7 +84,7 @@ const hillshadeUniformValues = (
 };
 
 const hillshadeUniformPrepareValues = (
-    tileID: OverscaledTileID, dem: DEMData, maxzoom: number
+    tileID: OverscaledTileID, dem: DEMData
 ): UniformValues<HillshadePrepareUniformsType> => {
 
     const stride = dem.stride;
@@ -100,7 +98,6 @@ const hillshadeUniformPrepareValues = (
         'u_image': 1,
         'u_dimension': [stride, stride],
         'u_zoom': tileID.overscaledZ,
-        'u_maxzoom': maxzoom,
         'u_unpack': dem.getUnpackVector()
     };
 };

src/shaders/hillshade_prepare.fragment.glsl

@@ -6,7 +6,6 @@ uniform sampler2D u_image;
 varying vec2 v_pos;
 uniform vec2 u_dimension;
 uniform float u_zoom;
-uniform float u_maxzoom;
 uniform vec4 u_unpack;
 
 float getElevation(vec2 coord, float bias) {
@@ -44,23 +43,25 @@ void main() {
     float h = getElevation(v_pos + vec2(0, epsilon.y), 0.0);
     float i = getElevation(v_pos + vec2(epsilon.x, epsilon.y), 0.0);
 
-    // here we divide the x and y slopes by 8 * pixel size
+    // Here we divide the x and y slopes by 8 * pixel size
     // where pixel size (aka meters/pixel) is:
     // circumference of the world / (pixels per tile * number of tiles)
     // which is equivalent to: 8 * 40075016.6855785 / (512 * pow(2, u_zoom))
-    // which can be reduced to: pow(2, 19.25619978527 - u_zoom)
-    // we want to vertically exaggerate the hillshading though, because otherwise
-    // it is barely noticeable at low zooms. to do this, we multiply this by some
-    // scale factor pow(2, (u_zoom - u_maxzoom) * a) where a is an arbitrary value
-    // Here we use a=0.3 which works out to the expression below. see 
-    // nickidlugash's awesome breakdown for more info
+    // which can be reduced to: pow(2, 19.25619978527 - u_zoom).
+    // We want to vertically exaggerate the hillshading because otherwise
+    // it is barely noticeable at low zooms. To do this, we multiply this by
+    // a scale factor that is a function of zooms below 15, which is an arbitrary
+    // that corresponds to the max zoom level of Mapbox terrain-RGB tiles.
+    // See nickidlugash's awesome breakdown for more info:
     // https://github.com/mapbox/mapbox-gl-js/pull/5286#discussion_r148419556
-    float exaggeration = u_zoom < 2.0 ? 0.4 : u_zoom < 4.5 ? 0.35 : 0.3;
+
+    float exaggerationFactor = u_zoom < 2.0 ? 0.4 : u_zoom < 4.5 ? 0.35 : 0.3;
+    float exaggeration = u_zoom < 15.0 ? (u_zoom - 15.0) * exaggerationFactor : 0.0;
 
     vec2 deriv = vec2(
         (c + f + f + i) - (a + d + d + g),
         (g + h + h + i) - (a + b + b + c)
-    ) /  pow(2.0, (u_zoom - u_maxzoom) * exaggeration + 19.2562 - u_zoom);
+    ) / pow(2.0, exaggeration + (19.2562 - u_zoom));
 
     gl_FragColor = clamp(vec4(
         deriv.x / 2.0 + 0.5,

test/integration/render-tests/hillshade-maxzoom/default/style.json

@@ -0,0 +1,36 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "height": 256,
+      "width": 256,
+      "description": "This test verifies that setting a lower maxzoom on the raster-dem source produces the same output as a higher maxzoom (hillshade-accent-color/default) when the map zoom level is lower than the maxzoom (i.e., maxzoom does not alter rendering at lower zooms)"
+    }
+  },
+  "center": [-113.26903, 35.9654],
+  "zoom": 11,
+  "sources": {
+    "source": {
+      "type": "raster-dem",
+      "tiles": [
+        "local://tiles/{z}-{x}-{y}.terrain.png"
+      ],
+      "maxzoom": 12,
+      "tileSize": 256
+    }
+  },
+  "layers": [
+    {
+      "id": "background",
+      "type": "background",
+      "paint": {
+        "background-color": "white"
+      }
+    },
+    {
+      "id": "hillshade",
+      "type": "hillshade",
+      "source": "source"
+    }
+  ]
+}

test/integration/render-tests/hillshade-maxzoom/overzoom/style.json

@@ -0,0 +1,36 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "height": 256,
+      "width": 256,
+      "description": "This test verifies that setting a maximum zoom on the raster-dem source lower than the layer results in overzooming the source."
+    }
+  },
+  "center": [-113.26903, 35.9654],
+  "zoom": 13,
+  "sources": {
+    "source": {
+      "type": "raster-dem",
+      "tiles": [
+        "local://tiles/{z}-{x}-{y}.terrain.png"
+      ],
+      "maxzoom": 12,
+      "tileSize": 256
+    }
+  },
+  "layers": [
+    {
+      "id": "background",
+      "type": "background",
+      "paint": {
+        "background-color": "white"
+      }
+    },
+    {
+      "id": "hillshade",
+      "type": "hillshade",
+      "source": "source"
+    }
+  ]
+}