[core] add maxzoom uniform for raster-dem tilesets (#11134)

* add maxzoom uniform to support external tilesets

* update git sha for gl-js

* try and fix android crash

* name default maxzoom constant

src/mbgl/programs/hillshade_prepare_program.hpp

@@ -10,6 +10,7 @@ namespace mbgl {
 
 namespace uniforms {
 MBGL_DEFINE_UNIFORM_VECTOR(uint16_t, 2, u_dimension);
+MBGL_DEFINE_UNIFORM_SCALAR(float, u_maxzoom);
 } // namespace uniforms
 
 class HillshadePrepareProgram : public Program<
@@ -22,6 +23,7 @@ class HillshadePrepareProgram : public Program<
         uniforms::u_matrix,
         uniforms::u_dimension,
         uniforms::u_zoom,
+        uniforms::u_maxzoom,
         uniforms::u_image>,
     style::Properties<>> {
 public:

src/mbgl/renderer/layers/render_hillshade_layer.cpp

@@ -1,6 +1,7 @@
 #include <mbgl/renderer/layers/render_hillshade_layer.hpp>
 #include <mbgl/renderer/buckets/hillshade_bucket.hpp>
 #include <mbgl/renderer/render_tile.hpp>
+#include <mbgl/renderer/sources/render_raster_dem_source.hpp>
 #include <mbgl/renderer/paint_parameters.hpp>
 #include <mbgl/renderer/render_static_data.hpp>
 #include <mbgl/programs/programs.hpp>
@@ -55,10 +56,14 @@ bool RenderHillshadeLayer::hasTransition() const {
     return unevaluated.hasTransition();
 }
 
-void RenderHillshadeLayer::render(PaintParameters& parameters, RenderSource*) {
+void RenderHillshadeLayer::render(PaintParameters& parameters, RenderSource* src) {
     if (parameters.pass != RenderPass::Translucent && parameters.pass != RenderPass::Pass3D)
         return;
     
+    RenderRasterDEMSource* demsrc = dynamic_cast<RenderRasterDEMSource*>(src);
+    const uint8_t TERRAIN_RGB_MAXZOOM = 15;
+    const uint8_t maxzoom = demsrc != nullptr ? demsrc->getMaxZoom() : TERRAIN_RGB_MAXZOOM;
+
     auto draw = [&] (const mat4& matrix,
                      const auto& vertexBuffer,
                      const auto& indexBuffer,
@@ -118,6 +123,7 @@ void RenderHillshadeLayer::render(PaintParameters& parameters, RenderSource*) {
                     uniforms::u_matrix::Value { mat },
                     uniforms::u_dimension::Value { {{uint16_t(tilesize * 2), uint16_t(tilesize * 2) }} },
                     uniforms::u_zoom::Value{ float(tile.id.canonical.z) },
+                    uniforms::u_maxzoom::Value{ float(maxzoom) },
                     uniforms::u_image::Value{ 0 }
                 },
                 parameters.staticData.rasterVertexBuffer,

src/mbgl/renderer/layers/render_hillshade_layer.hpp

@@ -16,7 +16,7 @@ public:
     void evaluate(const PropertyEvaluationParameters&) override;
     bool hasTransition() const override;
 
-    void render(PaintParameters&, RenderSource*) override;
+    void render(PaintParameters&, RenderSource* src) override;
 
     std::unique_ptr<Bucket> createBucket(const BucketParameters&, const std::vector<const RenderLayer*>&) const override;
 

src/mbgl/renderer/sources/render_raster_dem_source.cpp

@@ -36,7 +36,7 @@ void RenderRasterDEMSource::update(Immutable<style::Source::Impl> baseImpl_,
 
     if (tileset != _tileset) {
         tileset = _tileset;
-
+        maxzoom = tileset->zoomRange.max;
         // TODO: this removes existing buckets, and will cause flickering.
         // Should instead refresh tile data in place.
         tilePyramid.tiles.clear();

src/mbgl/renderer/sources/render_raster_dem_source.hpp

@@ -36,11 +36,16 @@ public:
     void reduceMemoryUse() final;
     void dumpDebugLogs() const final;
 
+    uint8_t getMaxZoom() const {
+        return maxzoom;
+    };
+
 private:
     const style::RasterSource::Impl& impl() const;
 
     TilePyramid tilePyramid;
     optional<Tileset> tileset;
+    uint8_t maxzoom = 15;
 
 protected:
     void onTileChanged(Tile&) final;

src/mbgl/shaders/hillshade_prepare.cpp

@@ -29,6 +29,7 @@ uniform sampler2D u_image;
 varying vec2 v_pos;
 uniform vec2 u_dimension;
 uniform float u_zoom;
+uniform float u_maxzoom;
 
 float getElevation(vec2 coord, float bias) {
     // Convert encoded elevation value to meters
@@ -71,16 +72,16 @@ void main() {
     // 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 - 14) * a) where a is an arbitrary value and 14 is the
-    // maxzoom of the tile source. here we use a=0.3 which works out to the
-    // expression below. see nickidlugash's awesome breakdown for more info
+    // 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
     // 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;
 
     vec2 deriv = vec2(
         (c + f + f + i) - (a + d + d + g),
         (g + h + h + i) - (a + b + b + c)
-    ) /  pow(2.0, (u_zoom - 14.0) * exaggeration + 19.2562 - u_zoom);
+    ) /  pow(2.0, (u_zoom - u_maxzoom) * exaggeration + 19.2562 - u_zoom);
 
     gl_FragColor = clamp(vec4(
         deriv.x / 2.0 + 0.5,