fix: GraphPoints shaders use valueForIndex functions

Author: Manfred Cheung

src/data/shaders/GraphPoints.fs.glsl

@@ -1,6 +1,6 @@
 #version 300 es
 precision highp float;
-precision highp isampler2D;
+precision lowp isampler2D;
 
 in vec2 vUv;
 
@@ -9,19 +9,7 @@ out vec4 fragColor;
 uniform sampler2D uPointTexture;
 uniform isampler2D uClassTexture;
 
-vec4 valueForIndex(sampler2D tex, int index) {
-    int texWidth = textureSize(tex, 0).x;
-    int col = index % texWidth;
-    int row = index / texWidth;
-    return texelFetch(tex, ivec2(col, row), 0);
-}
-
-ivec4 ivalueForIndex(isampler2D tex, int index) {
-    int texWidth = textureSize(tex, 0).x;
-    int col = index % texWidth;
-    int row = index / texWidth;
-    return texelFetch(tex, ivec2(col, row), 0);
-}
+#pragma glslify: import(../../renderer/shaders/valueForIndex.glsl)
 
 void main() {
     vec2 texSize = vec2(textureSize(uPointTexture, 0).xy);

src/renderer/shaders/valueForIndex.glsl

@@ -1,4 +1,5 @@
 precision lowp usampler2D;
+precision lowp isampler2D;
 
 vec4 valueForIndex(sampler2D tex, int index) {
     int texWidth = textureSize(tex, 0).x;
@@ -21,4 +22,11 @@ uint uivalueForIndex(usampler2D tex, int index) {
     return texelFetch(tex, ivec2(col, row), 0)[0];
 }
 
+ivec4 ivalueForIndex(isampler2D tex, int index) {
+    int texWidth = textureSize(tex, 0).x;
+    int col = index % texWidth;
+    int row = index / texWidth;
+    return texelFetch(tex, ivec2(col, row), 0);
+}
+
 #pragma glslify: export(valueForIndex)