Add minOpacity configuration option to heatmap.js and to heatmap-leaflet.js

Author: peluja1012

README.md

@@ -15,6 +15,7 @@ At the configuration object you can specify the following properties in order to
 - **visible** (optional) Boolean. Whether the heatmap is visible or not. Default is true
 - **gradient** (optional) Object. An object which contains colorstops from 0 to 1. Default is the standard heatmap gradient.
 - **opacity** (optional) Number [0-100]. Opacity of the heatmap measured in percent.
+- **minOpacity** (optional) Number [0-100]. Minimum opacity of the heatmap measured in percent. Default is 0 (transparent).
 
 Here is an example instanciation:
 

src/heatmap-leaflet.js

@@ -191,6 +191,7 @@
             "element": tile,
             "visible": true,
             "opacity": 100,  // we use leaflet's opacity for tiles
+            "minOpacity": options.minOpacity * 100,
             "gradient": options.gradient,
             "debug": options.debug
         });

src/heatmap.js

@@ -305,6 +305,7 @@
             max : false,
             gradient : false,
             opacity: 180,
+            minOpacity: 0,
             premultiplyAlpha: false,
             bounds: {
                 l: 1000,
@@ -342,6 +343,7 @@
                 me.set("max", config.max || false);
                 me.set("gradient", config.gradient || { 0.45: "rgb(0,0,255)", 0.55: "rgb(0,255,255)", 0.65: "rgb(0,255,0)", 0.95: "yellow", 1.0: "rgb(255,0,0)"});    // default is the common blue to red gradient
                 me.set("opacity", parseInt(255/(100/config.opacity), 10) || 180);
+                me.set("minOpacity", parseInt(255/(100/config.minOpacity), 10) || 0);
                 me.set("width", config.width || 0);
                 me.set("height", config.height || 0);
                 me.set("debug", config.debug);
@@ -464,6 +466,7 @@
                     premultiplyAlpha = me.get("premultiplyAlpha"),
                     palette = me.get("gradient"),
                     opacity = me.get("opacity"),
+                    minOpacity = me.get("minOpacity"),
                     bounds = me.get("bounds"),
                     left, top, bottom, right, 
                     image, imageData, length, alpha, offset, finalAlpha;
@@ -524,7 +527,14 @@
 
                     // we ve started with i=3
                     // set the new r, g and b values
-                    finalAlpha = (alpha < opacity)?alpha:opacity;
+                    if(alpha < minOpacity){
+                        finalAlpha = minOpacity;
+                    }else if(alpha > opacity){
+                        finalAlpha = opacity;
+                    }else{
+                        finalAlpha = alpha;
+                    }
+
                     imageData[i-3]=palette[offset];
                     imageData[i-2]=palette[offset+1];
                     imageData[i-1]=palette[offset+2];
@@ -537,7 +547,7 @@
                     	imageData[i-1] /= 255/finalAlpha;
                     }
 
-                    // we want the heatmap to have a gradient from transparent to the colors
+                    // we want the heatmap to have a gradient from transparent (or minOpacity, if specified) to the colors.
                     // as long as alpha is lower than the defined opacity (maximum), we'll use the alpha value
                     imageData[i] = finalAlpha;
                 }
@@ -650,4 +660,4 @@
         };
     })();
     w.h337 = w.heatmapFactory = heatmapFactory;
-})(window);
+})(window);