Fix shadow catcher (#330)

Author: slimbuck

src/shadow-catcher.ts

@@ -1,5 +1,5 @@
 import {
-    BLEND_MULTIPLICATIVE,
+    BLEND_PREMULTIPLIED,
     SHADOW_VSM_16F,
     SHADOWUPDATE_REALTIME as SHADOWUPDATE,
     AppBase,
@@ -12,6 +12,14 @@ import {
     StandardMaterial
 } from 'playcanvas';
 
+const litUserMainEndGLSL = `
+    gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0 - gl_FragColor.r);
+`;
+
+const litUserMainEndWGSL = `
+    output.color = vec4f(0.0, 0.0, 0.0, 1.0 - output.color.r);
+`;
+
 class ShadowCatcher {
     layer: Layer;
 
@@ -38,12 +46,16 @@ class ShadowCatcher {
 
         // create shadow catcher material
         this.material = new StandardMaterial();
+        this.material.blendType = BLEND_PREMULTIPLIED;
         this.material.shadowCatcher = true;
         this.material.useSkybox = false;
-        this.material.blendType = BLEND_MULTIPLICATIVE;
         this.material.depthWrite = false;
         this.material.diffuse.set(0, 0, 0);
         this.material.specular.set(0, 0, 0);
+
+        this.material.shaderChunks.glsl.set('litUserMainEndPS', litUserMainEndGLSL);
+        this.material.shaderChunks.wgsl.set('litUserMainEndPS', litUserMainEndWGSL);
+
         this.material.update();
 
         // create shadow catcher geometry

src/viewer.ts

@@ -725,6 +725,11 @@ class Viewer {
                     texture.type = TEXTURETYPE_RGBM;
                 }
                 this.initSkybox(texture);
+
+                // if we don't unload the texture asset and user selects it a second time, the
+                // brightness is completely wrong.
+                textureAsset.unload();
+                app.assets.remove(textureAsset);
             });
             app.assets.add(textureAsset);
             app.assets.load(textureAsset);