make text layers respect the translate-anchor

you can now specify "translate-anchor": "viewport" to have the text translated
in screen coordinates rather than relative to the tile. The default value
remains "translate-anchor": "map"

refs #189

include/llmr/renderer/painter.hpp

@@ -7,6 +7,7 @@
 #include <llmr/util/mat4.hpp>
 #include <llmr/util/noncopyable.hpp>
 #include <llmr/renderer/frame_history.hpp>
+#include <llmr/style/properties.hpp>
 
 #include <llmr/shader/plain_shader.hpp>
 #include <llmr/shader/outline_shader.hpp>
@@ -88,7 +89,8 @@ public:
     bool needsAnimation() const;
 private:
     void setupShaders();
-    void translateLayer(std::array<float, 2> translation, const Tile::ID &id, bool reverse = false);
+    void translateLayer(const std::array<float, 2> &translation, const Tile::ID &id, bool reverse = false);
+    mat4 translatedMatrix(const std::array<float, 2> &translation, const Tile::ID &id, TranslateAnchor anchor = TranslateAnchor::Map);
 
     void prepareTile(const Tile& tile);
     void useProgram(uint32_t program);

src/renderer/painter.cpp

@@ -171,7 +171,7 @@ void Painter::renderTileLayer(const Tile& tile, const LayerDescription &layer_de
     }
 }
 
-void Painter::translateLayer(const std::array<float, 2> translation, const Tile::ID &id, bool reverse) {
+void Painter::translateLayer(const std::array<float, 2> &translation, const Tile::ID &id, bool reverse) {
     if (translation[0] || translation[1]) {
         const int direction = reverse ? -1 : 1;
         // TODO: Get rid of the 8 (scaling from 4096 to tile size)
@@ -181,6 +181,32 @@ void Painter::translateLayer(const std::array<float, 2> translation, const Tile:
     }
 }
 
+mat4 Painter::translatedMatrix(const std::array<float, 2> &translation, const Tile::ID &id, TranslateAnchor anchor) {
+    if (translation[0] == 0 && translation[1] == 0) {
+        return matrix;
+    } else {
+        // TODO: Get rid of the 8 (scaling from 4096 to tile size)
+        const double factor = ((double)(1 << id.z)) / map.getState().getScale() /
+                              map.getState().getPixelRatio() * (4096.0 / util::tileSize);
+
+        mat4 result;
+        if (anchor == TranslateAnchor::Viewport) {
+            const double sin_a = sin(-map.getState().getAngle());
+            const double cos_a = cos(-map.getState().getAngle());
+            matrix::translate(result, matrix,
+                    factor * (translation[0] * cos_a - translation[1] * sin_a),
+                    factor * (translation[0] * sin_a + translation[1] * cos_a),
+                    0);
+        } else {
+            matrix::translate(result, matrix,
+                    factor * translation[0],
+                    factor * translation[1],
+                    0);
+        }
+        return result;
+    }
+}
+
 void Painter::renderMatte() {
     gl::group group("matte");
     glDisable(GL_DEPTH_TEST);

src/renderer/painter_text.cpp

@@ -16,8 +16,6 @@ void Painter::renderText(TextBucket& bucket, const std::string& layer_name, cons
     const TextProperties& properties = text_properties_it->second;
     if (!properties.enabled) return;
 
-    translateLayer(properties.translate, id);
-
     mat4 exMatrix;
     matrix::copy(exMatrix, projMatrix);
     if (bucket.geom_desc.path == TextPathType::Curve) {
@@ -33,8 +31,10 @@ void Painter::renderText(TextBucket& bucket, const std::string& layer_name, cons
     float fontSize = fmin(properties.size, bucket.geom_desc.font_size);
     matrix::scale(exMatrix, exMatrix, fontSize / 24.0f, fontSize / 24.0f, 1.0f);
 
+    const mat4 vtxMatrix = translatedMatrix(properties.translate, id, properties.translateAnchor);
+
     useProgram(textShader->program);
-    textShader->setMatrix(matrix);
+    textShader->setMatrix(vtxMatrix);
     textShader->setExtrudeMatrix(exMatrix);
 
     map.getGlyphAtlas().bind();
@@ -109,6 +109,4 @@ void Painter::renderText(TextBucket& bucket, const std::string& layer_name, cons
     textShader->setBuffer((256.0f - 64.0f) / 256.0f);
     glDepthRange(strata + strata_epsilon, 1.0f);
     bucket.drawGlyphs(*textShader);
-
-    translateLayer(properties.translate, id, true);
 }