Improve depth(for picking) bits precision

Author: tomlee-dev

src/framebuffer.ts

@@ -3,6 +3,7 @@ import { vec3 } from "gl-matrix";
 
 
 export class Framebuffer {
+    public static glContextStencilBits = 0; //class static variable
     public framebuffer: WebGLFramebuffer;
     public renderbuffer: WebGLRenderbuffer;
     public texture: WebGLTexture;
@@ -70,10 +71,17 @@ export class Framebuffer {
             gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
             gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
             gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
-            if (this._glVersion === 1) {
+
+            //If the stencil bit is 8 bits or more, set to record the depth texture with DEPTH24_STENCIL8 if available (24+8 expands to a total of 32 bits to record depth => needs confirmation)
+            if(Framebuffer.glContextStencilBits >= 8) {
+                //32bit(24+8) precision
+                gl.texImage2D(gl.TEXTURE_2D, 0, gl["DEPTH24_STENCIL8"], width, height, 0, gl.DEPTH_STENCIL, gl["UNSIGNED_INT_24_8"], null);
+            } else if (this._glVersion === 1) {
+                //8bit precision
                 gl.texImage2D(gl.TEXTURE_2D, 0, gl.DEPTH_COMPONENT, width, height, 0, gl.DEPTH_COMPONENT, gl.UNSIGNED_SHORT, null);
             } else {
-                gl.texImage2D(gl.TEXTURE_2D, 0, gl.DEPTH_COMPONENT16, width, height, 0, gl.DEPTH_COMPONENT, gl.UNSIGNED_SHORT, null);
+                //16bit precision
+                gl.texImage2D(gl.TEXTURE_2D, 0, gl.DEPTH_COMPONENT16, width, height, 0, gl.DEPTH_COMPONENT, gl.UNSIGNED_INT, null);
             }
         }
 
@@ -109,6 +117,23 @@ export class Framebuffer {
         return result;
     }
 
+    public getPixelAsFloat(x: number, y: number): number {
+        if (!this.isReady)
+            return null;
+        var result = new Uint8Array(4);
+        this.gl.readPixels(x, y, 1, 1, this.gl.RGBA, this.gl.UNSIGNED_BYTE, result);
+        return this.decodeFloatFromRGBA(result);
+    }
+
+    public decodeFloatFromRGBA(rgba : Uint8Array):number {
+        const rightVec4 = [1.0, 1/255.0, 1/65025.0, 1/16581375.0];
+        const dot =   (rgba[0] / 255.0) * rightVec4[0]
+                    + (rgba[1] / 255.0) * rightVec4[1]
+                    + (rgba[2] / 255.0) * rightVec4[2]
+                    + (rgba[3] / 255.0) * rightVec4[3];
+        return dot;
+    }
+
     public getDepth(x: number, y: number): number {
         if (!this.isReady)
             return null;
@@ -135,15 +160,12 @@ export class Framebuffer {
         const depths = this.getDepths(points);
 
         return depths.map((depth, i) => {
-            if (depth === 255) { // infinity (= nothing, no value)
-                return null;
-            }
 
             // convert values to clip space where x and y are [-1, 1] and z is [0, 1]
             const point = points[i];
             const xc = point.x / this.width * 2.0 - 1.0;
             const yc = point.y / this.height * 2.0 - 1.0;
-            const zc = (depth / 255.0 - 0.5) * 2.0;
+            const zc = (depth-0.5) * 2.0;
 
             return vec3.fromValues(xc, yc, zc);
         });
@@ -177,20 +199,13 @@ export class Framebuffer {
         }
 
         const depth = this.getDepth(x, y);
-        if (depth === 255) { // infinity
-            return null;
-        }
 
         // convert values to clip space where x and y are [-1, 1] and z is [0, 1]
         const xc = x / this.width * 2.0 - 1.0;
         const yc = y / this.height * 2.0 - 1.0;
-        const zc = (depth / 255.0 - 0.5) * 2.0;
-
-        const depthNear = Math.max(depth - 1, 0);
-        const zcn = (depthNear / 255.0 - 0.5) * 2.0;
-
-        const depthFar = Math.min(depth + 1, 255);
-        const zcf = (depthFar / 255.0 - 0.5) * 2.0;
+        const zc = 0.5;
+        const zcn = 0.0;
+        const zcf = 1.0;
 
         return {
             far: vec3.fromValues(xc, yc, zcf),

src/shaders/depth-reader.ts

@@ -41,7 +41,38 @@ export class DepthReader {
 
         //fragment shader
         this.fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
-        let fsCompiled = compile(this.fragmentShader, depth_fragment_shader);
+
+        const depth_fragment_shader_ws = `
+#ifdef GL_FRAGMENT_PRECISION_HIGH
+    precision highp float;
+    precision highp int;
+#else
+    precision mediump float;
+    precision mediump int;
+    #define highp mediump
+#endif
+
+varying vec2 position;
+uniform sampler2D texture;
+
+vec4 packDepth(float depth)
+{
+    // See Aras Pranckevičius' post Encoding Floats to RGBA
+    // http://aras-p.info/blog/2009/07/30/encoding-floats-to-rgba-the-final/
+    vec4 enc = vec4(1.0, 255.0, 65025.0, 16581375.0) * depth;
+    enc = fract(enc);
+    enc -= enc.yzww * vec4(1.0 / 255.0, 1.0 / 255.0, 1.0 / 255.0, 0.0);
+    return enc;
+}
+
+void main() {
+    float depth = texture2D(texture, position).x;
+    gl_FragColor = packDepth(texture2D(texture, position).r);
+    //[original code] gl_FragColor = vec4(depth, depth, depth, 1.0);
+}
+`;
+
+        let fsCompiled = compile(this.fragmentShader, depth_fragment_shader_ws); //change for ws
         if (!fsCompiled) {
             throw new Error("Failed to compile depth reading fragment shader");
         }
@@ -92,9 +123,8 @@ export class DepthReader {
         gl.enableVertexAttribArray(this.vertAttrs);
         gl.vertexAttribPointer(this.vertAttrs, 2, gl.FLOAT, false, 0, 0);
 
-
         gl.clearColor(0, 0, 0, 0); //zero colour for no-values
-        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
+        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT | gl.STENCIL_BUFFER_BIT);
 
         // draw the quad (2 triangles, 6 vertices)
         gl.drawArrays(gl.TRIANGLES, 0, 6);
@@ -112,7 +142,7 @@ export class DepthReader {
         this.draw(tex);
 
         // all components should be the same (therefore just using [0])
-        var depths = points.map(p => fb.getPixel(p.x, p.y)[0]) ;
+        var depths = points.map(p => fb.getPixelAsFloat(p.x, p.y)) ;
 
         // free resources
         fb.delete();

src/viewer.ts

@@ -376,7 +376,7 @@ export class Viewer {
         WebGLUtils.setupWebGL(this.canvas, (ctx, version) => {
             this.gl = ctx;
             this.glVersion = version;
-        }, { preserveDrawingBuffer: true }, (err) => {
+        }, { preserveDrawingBuffer: true, stencil: true}, (err) => {
             this.error(err);
         });
 
@@ -386,6 +386,8 @@ export class Viewer {
             return;
         }
 
+        let stencilBits = this.gl.getParameter(this.gl.STENCIL_BITS);
+        Framebuffer.glContextStencilBits = stencilBits;
 
         // keep reference to the function in case it gets into zone. For example Angular uses
         // NgZone forked from the root Zone to refresh data content. But we make heavy use of this