From 31f9a7110918b667932d4c28d8a4fee69d9390ca Mon Sep 17 00:00:00 2001
From: Aiosa <horakj7@gmail.com>
Date: Wed, 27 Sep 2023 15:16:23 +0200
Subject: [PATCH] Working tiledimage-level transparency in a single pass.

---
 src/webgl/drawer.js       | 25 +++++++++++++++++++++----
 src/webgl/renderer.js     |  8 +++++---
 src/webgl/webGLContext.js |  9 ++++++---
 3 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/src/webgl/drawer.js b/src/webgl/drawer.js
index 0da257b2..d0bbee3d 100644
--- a/src/webgl/drawer.js
+++ b/src/webgl/drawer.js
@@ -97,6 +97,11 @@ $.WebGL = class WebGL extends OpenSeadragon.DrawerBase {
 
         const engine = new $.WebGLModule($.extend(this.options, {
             uniqueId: "openseadragon",
+            "2.0": {
+                canvasOptions: {
+                    stencil: true
+                }
+            }
         }));
 
         engine.addRenderingSpecifications({
@@ -116,7 +121,7 @@ $.WebGL = class WebGL extends OpenSeadragon.DrawerBase {
         this.renderer = engine;
         this.renderer.setDataBlendingEnabled(true);
 
-        // const gl = this.renderer.gl;
+        const gl = this.renderer.gl;
         // this._renderToTexture = gl.createTexture();
         // gl.activeTexture(gl.TEXTURE0);
         // gl.bindTexture(gl.TEXTURE_2D, this._renderToTexture);
@@ -138,6 +143,10 @@ $.WebGL = class WebGL extends OpenSeadragon.DrawerBase {
         // gl.bindFramebuffer(gl.FRAMEBUFFER, this._glFrameBuffer);
         // gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, this._renderToTexture, 0);
 
+        gl.enable(gl.STENCIL_TEST);
+        gl.stencilMask(0xff);
+        gl.stencilFunc(gl.GREATER, 1, 0xff);
+        gl.stencilOp(gl.KEEP, gl.KEEP, gl.REPLACE);
         return engine.canvas;
     }
 
@@ -153,10 +162,11 @@ $.WebGL = class WebGL extends OpenSeadragon.DrawerBase {
             zoom: this.viewport.getZoom(true)
         };
 
-        let flipMultiplier = this.viewport.flipped ? -1 : 1;
+
+        // let flipMultiplier = this.viewport.flipped ? -1 : 1;
         // calculate view matrix for viewer
         let posMatrix = $.Mat3.makeTranslation(-viewport.center.x, -viewport.center.y);
-        let scaleMatrix = $.Mat3.makeScaling(2 / viewport.bounds.width * flipMultiplier, -2 / viewport.bounds.height);
+        let scaleMatrix = $.Mat3.makeScaling(2 / viewport.bounds.width, -2 / viewport.bounds.height);
         let rotMatrix = $.Mat3.makeRotation(-viewport.rotation);
         let viewMatrix = scaleMatrix.multiply(rotMatrix).multiply(posMatrix);
 
@@ -169,6 +179,12 @@ $.WebGL = class WebGL extends OpenSeadragon.DrawerBase {
         for (const tiledImage of tiledImages) {
             let tilesToDraw = tiledImage.getTilesToDraw();
 
+            if (tilesToDraw.length === 0) {
+                continue;
+            }
+
+            gl.clear(gl.STENCIL_BUFFER_BIT);
+
             let overallMatrix = viewMatrix;
             let imageRotation = tiledImage.getRotation(true);
             // if needed, handle the tiledImage being rotated
@@ -187,7 +203,7 @@ $.WebGL = class WebGL extends OpenSeadragon.DrawerBase {
             //todo better access to the rendering context
             const shader = this.renderer.specification(0).shaders.renderShader._renderContext;
             // iterate over tiles and add data for each one to the buffers
-            for (let tileIndex = 0; tileIndex < tilesToDraw.length; tileIndex++){
+            for (let tileIndex = tilesToDraw.length - 1; tileIndex >= 0; tileIndex--){
                 const tile = tilesToDraw[tileIndex].tile;
 
                 const matrix = this._getTileMatrix(tile, tiledImage, overallMatrix);
@@ -264,6 +280,7 @@ $.WebGL = class WebGL extends OpenSeadragon.DrawerBase {
             let localMatrix = t1.multiply($.Mat3.makeScaling(-1, 1)).multiply(t2);
             matrix = matrix.multiply(localMatrix);
         }
+
         let overallMatrix = viewMatrix.multiply(matrix);
         return overallMatrix.values;
     }
diff --git a/src/webgl/renderer.js b/src/webgl/renderer.js
index 7be24859..35d94f76 100644
--- a/src/webgl/renderer.js
+++ b/src/webgl/renderer.js
@@ -81,7 +81,6 @@ $.WebGLModule = class extends $.EventSource {
         this.visualisationInUse = function(visualisation) { };
         this.visualisationChanged = function(oldVis, newVis) { };
 
-
         /**
          * Debug mode.
          * @member {boolean}
@@ -124,12 +123,15 @@ $.WebGLModule = class extends $.EventSource {
         try {
             const canvas = document.createElement("canvas");
             for (let version of [this.webGlPreferredVersion, "2.0", "1.0"]) {
+                const contextOpts = incomingOptions[version] || {};
+
                 const Context = $.WebGLModule.determineContext(version);
-                let glContext = Context && Context.create(canvas);
+                //todo documment this
+                let glContext = Context && Context.create(canvas, contextOpts.canvasOptions || {});
 
                 if (glContext) {
                     this.gl = glContext;
-                    const contextOpts = incomingOptions[version] || {};
+
                     const readGlProp = function(prop, defaultValue) {
                         return glContext[contextOpts[prop] || defaultValue] || glContext[defaultValue];
                     };
diff --git a/src/webgl/webGLContext.js b/src/webgl/webGLContext.js
index 8056836c..4e92f4ad 100644
--- a/src/webgl/webGLContext.js
+++ b/src/webgl/webGLContext.js
@@ -60,9 +60,10 @@ $.WebGLModule.WebGLImplementation = class {
     /**
      * Static context creation (to avoid class instantiation in case of missing support)
      * @param canvas
+     * @param options desired options used in the canvas webgl context creation
      * @return {WebGLRenderingContextBase} //todo base is not common to all, remove from docs
      */
-    static create(canvas) {
+    static create(canvas, options) {
         throw("::create() must be implemented!");
     }
 
@@ -184,8 +185,10 @@ $.WebGLModule.WebGL20 = class extends $.WebGLModule.WebGLImplementation {
         return "2.0";
     }
 
-    static create(canvas) {
-        return canvas.getContext('webgl2', { premultipliedAlpha: true, alpha: true });
+    static create(canvas, options) {
+        options.alpha = true;
+        options.premultipliedAlpha = true;
+        return canvas.getContext('webgl2', options);
     }
 
     //todo try to implement on the global scope version-independntly