Review some shaders to work on GLSL 100

Tested on Raspberry Pi... Just note that platform is very limited by GPU...

examples/shaders/resources/shaders/glsl100/cubes_panning.fs

@@ -7,8 +7,8 @@ varying vec2 fragTexCoord;
 varying vec4 fragColor;
 
 // Custom variables
-#define PI 3.14159265358979323846
-uniform float uTime = 0.0;
+const float PI = 3.14159265358979323846;
+uniform float uTime;
 
 float divisions = 5.0;
 float angle = 0.0;
@@ -19,9 +19,9 @@ vec2 VectorRotateTime(vec2 v, float speed)
     float localTime = fract(time);  // The time domain this works on is 1 sec.
     
     if ((localTime >= 0.0) && (localTime < 0.25)) angle = 0.0;
-    else if ((localTime >= 0.25) && (localTime < 0.50)) angle = PI/4*sin(2*PI*localTime - PI/2);
+    else if ((localTime >= 0.25) && (localTime < 0.50)) angle = PI/4.0*sin(2.0*PI*localTime - PI/2.0);
     else if ((localTime >= 0.50) && (localTime < 0.75)) angle = PI*0.25;
-    else if ((localTime >= 0.75) && (localTime < 1.00)) angle = PI/4*sin(2*PI*localTime);
+    else if ((localTime >= 0.75) && (localTime < 1.00)) angle = PI/4.0*sin(2.0*PI*localTime);
     
     // Rotate vector by angle
     v -= 0.5;

examples/shaders/resources/shaders/glsl100/eratosthenes.fs

@@ -39,20 +39,22 @@ void main()
 {
 	vec4 color = vec4(1.0);
 	float scale = 1000.0; // Makes 100x100 square grid. Change this variable to make a smaller or larger grid.
-	int value = int(scale*floor(fragTexCoord.y*scale) + floor(fragTexCoord.x*scale));  // Group pixels into boxes representing integer values
-
-    if ((value == 0) || (value == 1) || (value == 2)) gl_FragColor = vec4(1.0);
-    else
+	float value = scale*floor(fragTexCoord.y*scale) + floor(fragTexCoord.x*scale);  // Group pixels into boxes representing integer values
+    int valuei = int(value);
+    
+    //if ((valuei == 0) || (valuei == 1) || (valuei == 2)) gl_FragColor = vec4(1.0);
+    //else
     {
-        for (int i = 2; (i < max(2, sqrt(value) + 1)); i++) 
+        //for (int i = 2; (i < int(max(2.0, sqrt(value) + 1.0))); i++)
+        // NOTE: On GLSL 100 for loops are restricted and loop condition must be a constant
+        // Tested on RPI, it seems loops are limited around 60 iteractions
+        for (int i = 2; i < 48; i++)
         {
-            if ((value - i*floor(value/i)) == 0) 
+            if ((value - float(i)*floor(value/float(i))) <= 0.0)
             {
-                color = Colorizer(float(i), scale);
+                gl_FragColor = Colorizer(float(i), scale);
                 //break;    // Uncomment to color by the largest factor instead
             }
         }
-
-        gl_FragColor = color;
     }
 }

examples/shaders/resources/shaders/glsl100/julia_set.fs

@@ -11,7 +11,9 @@ uniform vec2 c;                 // c.x = real, c.y = imaginary component. Equati
 uniform vec2 offset;            // Offset of the scale.
 uniform float zoom;             // Zoom of the scale.
 
-const int MAX_ITERATIONS = 255; // Max iterations to do.
+// NOTE: Maximum number of shader for-loop iterations depend on GPU,
+// for example, on RasperryPi for this examply only supports up to 60
+const int MAX_ITERATIONS = 48;  // Max iterations to do
 
 // Square a complex number
 vec2 ComplexSquare(vec2 z)
@@ -56,21 +58,22 @@ void main()
     // NOTE: fragTexCoord already comes as normalized screen coordinates but offset must be normalized before scaling and zoom
     vec2 z = vec2((fragTexCoord.x + offset.x/screenDims.x)*2.5/zoom, (fragTexCoord.y + offset.y/screenDims.y)*1.5/zoom);
 
-    int iterations = 0;
-    for (iterations = 0; iterations < MAX_ITERATIONS; iterations++)
+    int iter = 0;
+    for (int iterations = 0; iterations < 60; iterations++)
     {
         z = ComplexSquare(z) + c;  // Iterate function
-        
         if (dot(z, z) > 4.0) break;
+
+        iter = iterations;
     }
-    
+
     // Another few iterations decreases errors in the smoothing calculation.
     // See http://linas.org/art-gallery/escape/escape.html for more information.
     z = ComplexSquare(z) + c;
     z = ComplexSquare(z) + c;
     
     // This last part smooths the color (again see link above).
-    float smoothVal = float(iterations) + 1.0 - (log(log(length(z)))/log(2.0));
+    float smoothVal = float(iter) + 1.0 - (log(log(length(z)))/log(2.0));
     
     // Normalize the value so it is between 0 and 1.
     float norm = smoothVal/float(MAX_ITERATIONS);

examples/shaders/resources/shaders/glsl100/palette_switch.fs

@@ -15,15 +15,27 @@ uniform ivec3 palette[colors];
 void main()
 {
     // Texel color fetching from texture sampler
-    vec4 texelColor = texture2D(texture0, fragTexCoord) * fragColor;
+    vec4 texelColor = texture2D(texture0, fragTexCoord)*fragColor;
 
     // Convert the (normalized) texel color RED component (GB would work, too)
     // to the palette index by scaling up from [0, 1] to [0, 255].
-    int index = int(texelColor.r * 255.0);
-    ivec3 color = palette[index];
+    int index = int(texelColor.r*255.0);
+    
+    ivec3 color = ivec3(0);
+    
+    // NOTE: On GLSL 100 we are not allowed to index a uniform array by a variable value,
+    // a constantmust be used, so this logic...
+    if (index == 0) color = palette[0];
+    else if (index == 1) color = palette[1];
+    else if (index == 2) color = palette[2];
+    else if (index == 3) color = palette[3];
+    else if (index == 4) color = palette[4];
+    else if (index == 5) color = palette[5];
+    else if (index == 6) color = palette[6];
+    else if (index == 7) color = palette[7];
 
     // Calculate final fragment color. Note that the palette color components
     // are defined in the range [0, 255] and need to be normalized to [0, 1]
     // for OpenGL to work.
-    gl_FragColor = vec4(color / 255.0, texelColor.a);
+    gl_FragColor = vec4(float(color.x)/255.0, float(color.y)/255.0, float(color.z)/255.0, texelColor.a);
 }