Add PipelineManager#restoreContext method for restoring uniforms.

Also add `WebGLShader#syncUniforms` and other code necessary to retain
and reapply uniform state on the GPU.

src/renderer/webgl/PipelineManager.js

@@ -1248,6 +1248,24 @@ var PipelineManager = new Class({
         return this.set(this.FX_PIPELINE);
     },
 
+    /**
+     * Restore WebGL resources after context was lost.
+     * 
+     * Calls `rebind` on this Pipeline Manager.
+     * Then calls `restoreContext` on each pipeline in turn.
+     * 
+     * @method Phaser.Renderer.WebGL.PipelineManager#restoreContext
+     * @since 3.80.0
+     */
+    restoreContext: function ()
+    {
+        this.rebind();
+        this.pipelines.each(function (_, pipeline)
+        {
+            pipeline.restoreContext();
+        });
+    },
+
     /**
      * Use this to reset the gl context to the state that Phaser requires to continue rendering.
      *

src/renderer/webgl/WebGLPipeline.js

@@ -1194,6 +1194,24 @@ var WebGLPipeline = new Class({
         return this;
     },
 
+    /**
+     * This method is called if the WebGL context is lost and restored.
+     * It ensures that uniforms are synced back to the GPU
+     * for all shaders in this pipeline.
+     * 
+     * @method Phaser.Renderer.WebGL.WebGLPipeline#restoreContext
+     * @since 3.80.0
+     */
+    restoreContext: function ()
+    {
+        var shaders = this.shaders;
+
+        for (var i = 0; i < shaders.length; i++)
+        {
+            shaders[i].syncUniforms();
+        }
+    },
+
     /**
      * Binds the vertex buffer to be the active ARRAY_BUFFER on the WebGL context.
      *

src/renderer/webgl/WebGLShader.js

@@ -391,6 +391,7 @@ var WebGLShader = new Class({
                     {
                         name: name,
                         location: location,
+                        setter: null,
                         value1: null,
                         value2: null,
                         value3: null,
@@ -418,6 +419,7 @@ var WebGLShader = new Class({
                             {
                                 name: name,
                                 location: location,
+                                setter: null,
                                 value1: null,
                                 value2: null,
                                 value3: null,
@@ -432,6 +434,25 @@ var WebGLShader = new Class({
         return this;
     },
 
+    /**
+     * Repopulate uniforms on the GPU.
+     * 
+     * This is called automatically by the pipeline when the context is
+     * lost and then recovered. By the time this method is called,
+     * the WebGL resources are already recreated, so we just need to
+     * re-populate them.
+     * 
+     * @method Phaser.Renderer.WebGL.WebGLShader#syncUniforms
+     * @since 3.80.0
+     */
+    syncUniforms: function ()
+    {
+        ArrayEach(this.uniforms, function (uniform)
+        {
+            uniform.setter.call(this.gl, uniform.location.webGLUniformLocation, uniform.value1, uniform.value2, uniform.value3, uniform.value4);
+        });
+    },
+
     /**
      * Checks to see if the given uniform name exists and is active in this shader.
      *
@@ -504,6 +525,11 @@ var WebGLShader = new Class({
 
         if (skipCheck || uniform.value1 !== value1)
         {
+            if (!uniform.setter)
+            {
+                uniform.setter = setter;
+            }
+
             uniform.value1 = value1;
 
             this.renderer.setProgram(this.program);
@@ -549,6 +575,11 @@ var WebGLShader = new Class({
 
         if (skipCheck || uniform.value1 !== value1 || uniform.value2 !== value2)
         {
+            if (!uniform.setter)
+            {
+                uniform.setter = setter;
+            }
+
             uniform.value1 = value1;
             uniform.value2 = value2;
 
@@ -596,6 +627,11 @@ var WebGLShader = new Class({
 
         if (skipCheck || uniform.value1 !== value1 || uniform.value2 !== value2 || uniform.value3 !== value3)
         {
+            if (!uniform.setter)
+            {
+                uniform.setter = setter;
+            }
+
             uniform.value1 = value1;
             uniform.value2 = value2;
             uniform.value3 = value3;
@@ -645,6 +681,11 @@ var WebGLShader = new Class({
 
         if (skipCheck || uniform.value1 !== value1 || uniform.value2 !== value2 || uniform.value3 !== value3 || uniform.value4 !== value4)
         {
+            if (!uniform.setter)
+            {
+                uniform.setter = setter;
+            }
+
             uniform.value1 = value1;
             uniform.value2 = value2;
             uniform.value3 = value3;

src/renderer/webgl/typedefs/WebGLPipelineUniformsConfig.js

@@ -4,6 +4,7 @@
  *
  * @property {string} name - The name of the uniform as defined in the shader.
  * @property {number} location - The location of the uniform.
+ * @property {?function} setter - The setter function called on the WebGL context to set the uniform value.
  * @property {number} [value1] - The first cached value of the uniform.
  * @property {number} [value2] - The first cached value of the uniform.
  * @property {number} [value3] - The first cached value of the uniform.