Fix touching color check for background color

Author: adroitwhiz

src/RenderWebGL.js

@@ -182,9 +182,23 @@ class RenderWebGL extends EventEmitter {
         /** @type {function} */
         this._exitRegion = null;
 
+        /** @type {object} */
+        this._backgroundDrawRegionId = {
+            enter: () => this._enterDrawBackground(),
+            exit: () => this._exitDrawBackground()
+        };
+
         /** @type {Array.<snapshotCallback>} */
         this._snapshotCallbacks = [];
 
+        /** @type {Array<number>}
+         * @readonly */
+        this._backgroundColor4f = [0, 0, 0, 0];
+
+        /** @type {Uint8ClampedArray}
+         * @readonly */
+        this._backgroundColor3b = new Uint8ClampedArray(3);
+
         this._createGeometry();
 
         this.on(RenderConstants.Events.NativeSizeChanged, this.onNativeSizeChanged);
@@ -244,7 +258,12 @@ class RenderWebGL extends EventEmitter {
      * @param {number} blue The blue component for the background.
      */
     setBackgroundColor (red, green, blue) {
-        this._backgroundColor = [red, green, blue, 1];
+        this._backgroundColor4f = [red, green, blue, 1];
+
+        this._backgroundColor3b[0] = red * 255;
+        this._backgroundColor3b[1] = green * 255;
+        this._backgroundColor3b[2] = blue * 255;
+
     }
 
     /**
@@ -623,7 +642,7 @@ class RenderWebGL extends EventEmitter {
 
         twgl.bindFramebufferInfo(gl, null);
         gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
-        gl.clearColor.apply(gl, this._backgroundColor);
+        gl.clearColor.apply(gl, this._backgroundColor4f);
         gl.clear(gl.COLOR_BUFFER_BIT);
 
         this._drawThese(this._drawList, ShaderManager.DRAW_MODE.default, this._projection);
@@ -739,12 +758,20 @@ class RenderWebGL extends EventEmitter {
      */
     isTouchingColor (drawableID, color3b, mask3b) {
         const candidates = this._candidatesTouching(drawableID, this._visibleDrawList);
-        if (candidates.length === 0) {
+
+        let bounds;
+        if (colorMatches(color3b, this._backgroundColor3b, 0)) {
+            // If the color we're checking for is the background color, don't confine the check to
+            // candidate drawables' bounds--since the background spans the entire stage, we must check
+            // everything that lies inside the drawable.
+            bounds = this._touchingBounds(drawableID);
+        } else if (candidates.length === 0) {
+            // If not checking for the background color, we can return early if there are no candidate drawables.
             return false;
+        } else {
+            bounds = this._candidatesBounds(candidates);
         }
 
-        const bounds = this._candidatesBounds(candidates);
-
         const maxPixelsForCPU = this._getMaxPixelsForCPU();
 
         const debugCanvasContext = this._debugCanvas && this._debugCanvas.getContext('2d');
@@ -805,6 +832,19 @@ class RenderWebGL extends EventEmitter {
         }
     }
 
+    _enterDrawBackground () {
+        const gl = this.gl;
+        const currentShader = this._shaderManager.getShader(ShaderManager.DRAW_MODE.background, 0);
+        gl.disable(gl.BLEND);
+        gl.useProgram(currentShader.program);
+        twgl.setBuffersAndAttributes(gl, currentShader, this._bufferInfo);
+    }
+
+    _exitDrawBackground () {
+        const gl = this.gl;
+        gl.enable(gl.BLEND);
+    }
+
     _isTouchingColorGpuStart (drawableID, candidateIDs, bounds, color3b, mask3b) {
         this._doExitDrawRegion();
 
@@ -816,15 +856,8 @@ class RenderWebGL extends EventEmitter {
         gl.viewport(0, 0, bounds.width, bounds.height);
         const projection = twgl.m4.ortho(bounds.left, bounds.right, bounds.top, bounds.bottom, -1, 1);
 
-        let fillBackgroundColor = this._backgroundColor;
-
-        // When using masking such that the background fill color will showing through, ensure we don't
-        // fill using the same color that we are trying to detect!
-        if (color3b[0] > 196 && color3b[1] > 196 && color3b[2] > 196) {
-            fillBackgroundColor = [0, 0, 0, 255];
-        }
-
-        gl.clearColor.apply(gl, fillBackgroundColor);
+        // Clear the query buffer to fully transparent. This will be the color of pixels that fail the stencil test.
+        gl.clearColor(0, 0, 0, 0);
         gl.clear(gl.COLOR_BUFFER_BIT | gl.STENCIL_BUFFER_BIT);
 
         let extraUniforms;
@@ -835,7 +868,11 @@ class RenderWebGL extends EventEmitter {
             };
         }
 
+        // TODO: figure out why this is all in a try block?
         try {
+            // Using the stencil buffer, mask out the drawing to either the drawable's bounds
+            // or pixels of the drawable which match the mask color, depending on whether a mask color is given.
+            // Masked-out pixels will not be checked.
             gl.enable(gl.STENCIL_TEST);
             gl.stencilFunc(gl.ALWAYS, 1, 1);
             gl.stencilOp(gl.KEEP, gl.KEEP, gl.REPLACE);
@@ -856,6 +893,18 @@ class RenderWebGL extends EventEmitter {
             gl.stencilOp(gl.KEEP, gl.KEEP, gl.KEEP);
             gl.colorMask(true, true, true, true);
 
+            // Draw the background as a quad. Drawing a background with gl.clear will not mask to the stenciled area.
+            this.enterDrawRegion(this._backgroundDrawRegionId);
+
+            const uniforms = {
+                u_backgroundColor: this._backgroundColor4f
+            };
+
+            const currentShader = this._shaderManager.getShader(ShaderManager.DRAW_MODE.background, 0);
+            twgl.setUniforms(currentShader, uniforms);
+            twgl.drawBufferInfo(gl, this._bufferInfo, gl.TRIANGLES);
+
+            // Draw the candidate drawables on top of the background.
             this._drawThese(candidateIDs, ShaderManager.DRAW_MODE.default, projection,
                 {idFilterFunc: testID => testID !== drawableID}
             );
@@ -880,7 +929,8 @@ class RenderWebGL extends EventEmitter {
         }
 
         for (let pixelBase = 0; pixelBase < pixels.length; pixelBase += 4) {
-            if (colorMatches(color3b, pixels, pixelBase)) {
+            // Transparent pixels are masked (either by the drawable's bounds or color mask).
+            if (pixels[pixelBase + 3] !== 0 && colorMatches(color3b, pixels, pixelBase)) {
                 return true;
             }
         }
@@ -1210,7 +1260,7 @@ class RenderWebGL extends EventEmitter {
         gl.viewport(0, 0, bounds.width, bounds.height);
         const projection = twgl.m4.ortho(bounds.left, bounds.right, bounds.top, bounds.bottom, -1, 1);
 
-        gl.clearColor.apply(gl, this._backgroundColor);
+        gl.clearColor.apply(gl, this._backgroundColor4f);
         gl.clear(gl.COLOR_BUFFER_BIT);
         this._drawThese(this._drawList, ShaderManager.DRAW_MODE.default, projection);
 

src/ShaderManager.js

@@ -176,7 +176,12 @@ ShaderManager.DRAW_MODE = {
     /**
      * Draw a line with caps.
      */
-    line: 'line'
+    line: 'line',
+
+    /**
+     * Draw the background in a certain color. Must sometimes be used instead of gl.clear.
+     */
+    background: 'background'
 };
 
 module.exports = ShaderManager;

src/shaders/sprite.frag

@@ -39,6 +39,10 @@ uniform float u_lineThickness;
 uniform vec4 u_penPoints;
 #endif // DRAW_MODE_line
 
+#ifdef DRAW_MODE_background
+uniform vec4 u_backgroundColor;
+#endif // DRAW_MODE_background
+
 uniform sampler2D u_skin;
 
 varying vec2 v_texCoord;
@@ -109,7 +113,7 @@ const vec2 kCenter = vec2(0.5, 0.5);
 
 void main()
 {
-	#ifndef DRAW_MODE_line
+	#if !(defined(DRAW_MODE_line) || defined(DRAW_MODE_background))
 	vec2 texcoord0 = v_texCoord;
 
 	#ifdef ENABLE_mosaic
@@ -215,7 +219,9 @@ void main()
 	gl_FragColor.rgb /= gl_FragColor.a + epsilon;
 	#endif
 
-	#else // DRAW_MODE_line
+	#endif // !(defined(DRAW_MODE_line) || defined(DRAW_MODE_background))
+
+	#ifdef DRAW_MODE_line
 	// Maaaaagic antialiased-line-with-round-caps shader.
 	// Adapted from Inigo Quilez' 2D distance function cheat sheet
 	// https://www.iquilezles.org/www/articles/distfunctions2d/distfunctions2d.htm
@@ -251,4 +257,8 @@ void main()
 
 	gl_FragColor = u_lineColor * cappedLine;
 	#endif // DRAW_MODE_line
+
+	#ifdef DRAW_MODE_background
+	gl_FragColor = u_backgroundColor;
+	#endif
 }

src/shaders/sprite.vert

@@ -56,6 +56,9 @@ void main() {
 
 	gl_Position = vec4(position, 0, 1);
 	v_texCoord = position * 0.5 * u_stageSize;
+	#elif defined(DRAW_MODE_background)
+	gl_Position = vec4(a_position * 2.0, 0, 1);
+	v_texCoord = a_texCoord;
 	#else
 	gl_Position = u_projectionMatrix * u_modelMatrix * vec4(a_position, 0, 1);
 	v_texCoord = a_texCoord;