Fix highp samplers issues

CHANGES.md

@@ -1,5 +1,11 @@
 # Change Log
 
+### 1.73 - 2020-09-01
+
+##### Fixes :wrench:
+
+- Fixed several artifcats on mobile devices caused by using insufficient precision. [#9064](https://github.com/CesiumGS/cesium/pull/9064)
+
 ### 1.72 - 2020-08-03
 
 ##### Breaking Changes :mega:

Source/Renderer/ShaderSource.js

@@ -235,12 +235,16 @@ function combineShader(shaderSource, isFragmentShader, context) {
   }
 
   if (isFragmentShader) {
+    // If high precision isn't support replace occurrences of highp with mediump
+    // The highp keyword is not always available on older mobile devices
+    // See https://developer.mozilla.org/en-US/docs/Web/API/WebGL_API/WebGL_best_practices#In_WebGL_1_highp_float_support_is_optional_in_fragment_shaders
     result +=
       "\
 #ifdef GL_FRAGMENT_PRECISION_HIGH\n\
     precision highp float;\n\
 #else\n\
     precision mediump float;\n\
+    #define highp mediump\n\
 #endif\n\n";
   }
 

Source/Scene/GlobeDepth.js

@@ -76,7 +76,7 @@ function executeDebugGlobeDepth(globeDepth, context, passState, useLogDepth) {
     useLogDepth !== globeDepth._useLogDepth
   ) {
     var fsSource =
-      "uniform sampler2D u_depthTexture;\n" +
+      "uniform highp sampler2D u_depthTexture;\n" +
       "varying vec2 v_textureCoordinates;\n" +
       "void main()\n" +
       "{\n" +

Source/Scene/PickDepth.js

@@ -29,7 +29,7 @@ function executeDebugPickDepth(pickDepth, context, passState, useLogDepth) {
     useLogDepth !== pickDepth._useLogDepth
   ) {
     var fsSource =
-      "uniform sampler2D u_texture;\n" +
+      "uniform highp sampler2D u_texture;\n" +
       "varying vec2 v_textureCoordinates;\n" +
       "void main()\n" +
       "{\n" +
@@ -116,7 +116,7 @@ function updateFramebuffers(pickDepth, context, depthTexture) {
 function updateCopyCommands(pickDepth, context, depthTexture) {
   if (!defined(pickDepth._copyDepthCommand)) {
     var fs =
-      "uniform sampler2D u_texture;\n" +
+      "uniform highp sampler2D u_texture;\n" +
       "varying vec2 v_textureCoordinates;\n" +
       "void main()\n" +
       "{\n" +

Source/Shaders/Builtin/Functions/shadowDepthCompare.glsl

@@ -1,10 +1,10 @@
 
-float czm_sampleShadowMap(samplerCube shadowMap, vec3 d)
+float czm_sampleShadowMap(highp samplerCube shadowMap, vec3 d)
 {
     return czm_unpackDepth(textureCube(shadowMap, d));
 }
 
-float czm_sampleShadowMap(sampler2D shadowMap, vec2 uv)
+float czm_sampleShadowMap(highp sampler2D shadowMap, vec2 uv)
 {
 #ifdef USE_SHADOW_DEPTH_TEXTURE
     return texture2D(shadowMap, uv).r;

Source/Shaders/PostProcessStages/PassThroughDepth.glsl

@@ -1,4 +1,4 @@
-uniform sampler2D u_depthTexture;
+uniform highp sampler2D u_depthTexture;
 
 varying vec2 v_textureCoordinates;