Review shader to use provided texture coordinates

Now shader uses `fragTexCoord` that are the full screen texture coordinates normalized, instead of `gl_fragCoord`, the unnormalized screen coordinates

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

@@ -33,13 +33,6 @@ vec3 Hsv2rgb(vec3 c)
 
 void main()
 {
-    // The pixel coordinates scaled so they are on the mandelbrot scale
-    // y also flipped due to opengl
-    vec2 z = vec2((((gl_FragCoord.x + offset.x)/screenDims.x)*2.5)/zoom,
-                  (((screenDims.y - gl_FragCoord.y + offset.y)/screenDims.y)*1.5)/zoom);
-                  
-    int iterations = 0;
-
     /**********************************************************************************************
       Julia sets use a function z^2 + c, where c is a constant.
       This function is iterated until the nature of the point is determined.
@@ -58,6 +51,12 @@ void main()
       We use dot product (z.x * z.x + z.y * z.y) to determine the magnitude (length) squared.
       And once the magnitude squared is > 4, then magnitude > 2 is also true (saves computational power).
     *************************************************************************************************/
+    
+    // The pixel coordinates are scaled so they are on the mandelbrot scale
+    // 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++)
     {
         z = ComplexSquare(z) + c;  // Iterate function

examples/shaders/resources/shaders/glsl330/julia_set.fs

@@ -33,13 +33,6 @@ vec3 Hsv2rgb(vec3 c)
 
 void main()
 {
-    // The pixel coordinates scaled so they are on the mandelbrot scale
-    // y also flipped due to opengl
-    vec2 z = vec2((((gl_FragCoord.x + offset.x)/screenDims.x)*2.5)/zoom,
-                  (((screenDims.y - gl_FragCoord.y + offset.y)/screenDims.y)*1.5)/zoom);
-                  
-    int iterations = 0;
-
     /**********************************************************************************************
       Julia sets use a function z^2 + c, where c is a constant.
       This function is iterated until the nature of the point is determined.
@@ -58,6 +51,12 @@ void main()
       We use dot product (z.x * z.x + z.y * z.y) to determine the magnitude (length) squared.
       And once the magnitude squared is > 4, then magnitude > 2 is also true (saves computational power).
     *************************************************************************************************/
+    
+    // The pixel coordinates are scaled so they are on the mandelbrot scale
+    // 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++)
     {
         z = ComplexSquare(z) + c;  // Iterate function

examples/shaders/shaders_julia_set.c

@@ -153,15 +153,18 @@ int main()
             BeginTextureMode(target);       // Enable drawing to texture
                 ClearBackground(BLACK);     // Clear the render texture
 
-                // Draw a rectangle in shader mode
-                // NOTE: This acts as a canvas for the shader to draw on
-                BeginShaderMode(shader);
+                // Draw a rectangle in shader mode to be used as shader canvas
+                // NOTE: Rectangle uses font white character texture coordinates,
+                // so shader can not be applied here directly because input vertexTexCoord
+                // do not represent full screen coordinates (space where want to apply shader)
                 DrawRectangle(0, 0, GetScreenWidth(), GetScreenHeight(), BLACK);
-                EndShaderMode();
             EndTextureMode();
 
-            // Draw the saved texture (rendered julia set)
-            DrawTextureRec(target.texture, (Rectangle){ 0, 0, target.texture.width, -target.texture.height }, (Vector2){ 0.0f, 0.0f }, WHITE);
+            // Draw the saved texture and rendered julia set with shader
+            // NOTE: We do not invert texture on Y, already considered inside shader
+            BeginShaderMode(shader);
+                DrawTexture(target.texture, 0, 0, WHITE);
+            EndShaderMode();
                 
             if (showControls)
             {