add strokeBlur property (default 1.0, larger values blur more) to achieve a gradient effect

fixes #194

include/llmr/style/properties.hpp

@@ -131,6 +131,7 @@ struct TextClass {
     Color color = {{ 0, 0, 0, 1 }};
     Color halo = {{ 1, 1, 1, 0.75 }};
     FunctionProperty haloRadius = 0.25f;
+    FunctionProperty haloBlur = 1.0f;
     FunctionProperty size = 12.0f;
     FunctionProperty rotate = 0.0f;
     FunctionProperty alwaysVisible = false;
@@ -144,6 +145,7 @@ struct TextProperties {
     Color color = {{ 0, 0, 0, 1 }};
     Color halo = {{ 1, 1, 1, 0.75 }};
     float haloRadius = 0.25f;
+    float haloBlur = 1.0f;
     float size = 12.0f;
     float rotate = 0.0f;
     bool alwaysVisible = false;

src/renderer/painter_text.cpp

@@ -41,8 +41,6 @@ void Painter::renderText(TextBucket& bucket, const std::string& layer_name, cons
     textShader->setTextureSize({{static_cast<float>(map.getGlyphAtlas().width),
                                  static_cast<float>(map.getGlyphAtlas().height)}});
 
-    textShader->setGamma(2.5f / fontSize / map.getState().getPixelRatio());
-
     // Convert the -pi..pi to an int8 range.
     float angle = round((map.getState().getAngle() + rotate) / M_PI * 128);
 
@@ -98,15 +96,19 @@ void Painter::renderText(TextBucket& bucket, const std::string& layer_name, cons
     // We're drawing in the translucent pass which is bottom-to-top, so we need
     // to draw the halo first.
     if (properties.halo[3] > 0.0f) {
+        textShader->setGamma(properties.haloBlur * 2.4f / fontSize / map.getState().getPixelRatio());
         textShader->setColor(properties.halo);
         textShader->setBuffer(properties.haloRadius);
         glDepthRange(strata, 1.0f);
         bucket.drawGlyphs(*textShader);
     }
 
-    // Then, we draw the text over the halo
-    textShader->setColor(properties.color);
-    textShader->setBuffer((256.0f - 64.0f) / 256.0f);
-    glDepthRange(strata + strata_epsilon, 1.0f);
-    bucket.drawGlyphs(*textShader);
+    if (properties.color[3] > 0.0f) {
+        // Then, we draw the text over the halo
+        textShader->setGamma(2.4f / fontSize / map.getState().getPixelRatio());
+        textShader->setColor(properties.color);
+        textShader->setBuffer((256.0f - 64.0f) / 256.0f);
+        glDepthRange(strata + strata_epsilon, 1.0f);
+        bucket.drawGlyphs(*textShader);
+    }
 }

src/style/style.cpp

@@ -102,6 +102,7 @@ void Style::cascade(float z) {
             text.size = layer.size.evaluate<float>(z);
             text.halo = layer.halo;
             text.haloRadius = layer.haloRadius.evaluate<float>(z);
+            text.haloBlur = layer.haloBlur.evaluate<float>(z);
             text.rotate = layer.rotate.evaluate<float>(z);
             text.alwaysVisible = layer.alwaysVisible.evaluate<bool>(z);
             text.opacity = layer.opacity.evaluate<float>(z);

src/style/style_parser.cpp

@@ -571,6 +571,10 @@ TextClass StyleParser::parseTextClass(JSVal value) {
         klass.haloRadius = parseFunction(value["strokeWidth"]);
     }
 
+    if (value.HasMember("strokeBlur")) {
+        klass.haloBlur = parseFunction(value["strokeBlur"]);
+    }
+
     if (value.HasMember("size")) {
         klass.size = parseFunction(value["size"]);
     }