Update shaders_game_of_life.c

* Fix modulo bias in GetRandomValue(); implement rejection sampling for uniformity

* Replace do-while with for-loop in GetRandomValue rejection sampling

examples/shaders/shaders_game_of_life.c

@@ -61,6 +61,8 @@ int main(void)
     const int screenWidth = 800;
     const int screenHeight = 450;
     
+    InitWindow(screenWidth, screenHeight, "raylib [shaders] example - game of life");
+
     const int menuWidth = 100;
     const int windowWidth = screenWidth - menuWidth;
     const int windowHeight = screenHeight;
@@ -80,10 +82,9 @@ int main(void)
         { "Puffer train", "puffer_train", { 0.1f, 0.5f } }, { "Glider Gun", "glider_gun", { 0.2f, 0.2f } }, { "Breeder", "breeder", { 0.1f, 0.5f } },
         { "Random", "", { 0.5f, 0.5f } }
     };
-    const int numberOfPresets = sizeof(presetPatterns) / sizeof(presetPatterns[0]);
     
-    // Variable declaration
-    //--------------------------------------------------------------------------------------
+    const int numberOfPresets = sizeof(presetPatterns)/sizeof(presetPatterns[0]);
+
     int zoom = 1;
     float offsetX = (worldWidth - windowWidth)/2.0f;    // Centered on window
     float offsetY = (worldHeight - windowHeight)/2.0f;  // Centered on window
@@ -97,8 +98,6 @@ int main(void)
     bool buttonFaster = false;
     bool buttonSlower = false;
 
-    InitWindow(screenWidth, screenHeight, "raylib [shaders] example - game of life");
-
     // Load shader
     Shader shdrGameOfLife = LoadShader(0, TextFormat("resources/shaders/glsl%i/game_of_life.fs", GLSL_VERSION));
 
@@ -115,7 +114,7 @@ int main(void)
     EndTextureMode();
 
     Image startPattern = LoadImage("resources/game_of_life/r_pentomino.png");
-    UpdateTextureRec(world2.texture, (Rectangle) { worldWidth / 2.0f, worldHeight / 2.0f, (float)(startPattern.width), (float)(startPattern.height) }, startPattern.data);
+    UpdateTextureRec(world2.texture, (Rectangle){ worldWidth/2.0f, worldHeight/2.0f, (float)(startPattern.width), (float)(startPattern.height) }, startPattern.data);
     UnloadImage(startPattern);
 
     // Pointers to the two textures, to be swapped
@@ -143,10 +142,8 @@ int main(void)
 
             const float centerX = offsetX + (windowWidth/2.0f)/zoom;
             const float centerY = offsetY + (windowHeight/2.0f)/zoom;
-            if (buttonZoomIn || (mouseWheelMove > 0.0f))
-                zoom *= 2;
-            if ((buttonZomOut || (mouseWheelMove < 0.0f)) && (zoom > 1))
-                zoom /= 2;
+            if (buttonZoomIn || (mouseWheelMove > 0.0f)) zoom *= 2;
+            if ((buttonZomOut || (mouseWheelMove < 0.0f)) && (zoom > 1)) zoom /= 2;
             offsetX = centerX - (windowWidth/2.0f)/zoom;
             offsetY = centerY - (windowHeight/2.0f)/zoom;
         }
@@ -156,7 +153,6 @@ int main(void)
         if (buttonSlower)                         framesPerStep++;
 
         // Mouse management
-        //----------------------------------------------------------------------------------
         if ((mode == MODE_RUN) || (mode == MODE_PAUSE))
         {
             FreeImageToDraw(&imageToDraw);  // Free the image to draw: no longer needed in these modes
@@ -177,10 +173,8 @@ int main(void)
             const float offsetDecimalY = offsetY - floorf(offsetY);
             int sizeInWorldX = (int)(ceilf((float)(windowWidth + offsetDecimalX*zoom)/zoom));
             int sizeInWorldY = (int)(ceilf((float)(windowHeight + offsetDecimalY*zoom)/zoom));
-            if (offsetX + sizeInWorldX >= worldWidth)
-                sizeInWorldX = worldWidth - (int)floorf(offsetX);
-            if (offsetY + sizeInWorldY >= worldHeight)
-                sizeInWorldY = worldHeight - (int)floorf(offsetY);
+            if (offsetX + sizeInWorldX >= worldWidth) sizeInWorldX = worldWidth - (int)floorf(offsetX);
+            if (offsetY + sizeInWorldY >= worldHeight) sizeInWorldY = worldHeight - (int)floorf(offsetY);
 
             // Create image to draw if not created yet
             if (imageToDraw == NULL)
@@ -192,6 +186,7 @@ int main(void)
                 EndTextureMode();
                 imageToDraw = (Image*)RL_MALLOC(sizeof(Image));
                 *imageToDraw = LoadImageFromTexture(worldOnScreen.texture);
+                
                 UnloadRenderTexture(worldOnScreen);
             }
 
@@ -201,32 +196,30 @@ int main(void)
             {
                 int mouseX = (int)(mousePosition.x + offsetDecimalX*zoom)/zoom;
                 int mouseY = (int)(mousePosition.y + offsetDecimalY*zoom)/zoom;
-                if (mouseX >= sizeInWorldX)
-                    mouseX = sizeInWorldX - 1;
-                if (mouseY >= sizeInWorldY)
-                    mouseY = sizeInWorldY - 1;
-                if (firstColor == -1)
-                    firstColor = (GetImageColor(*imageToDraw, mouseX, mouseY).r < 5)? 0 : 1;
+                if (mouseX >= sizeInWorldX) mouseX = sizeInWorldX - 1;
+                if (mouseY >= sizeInWorldY) mouseY = sizeInWorldY - 1;
+                if (firstColor == -1) firstColor = (GetImageColor(*imageToDraw, mouseX, mouseY).r < 5)? 0 : 1;
                 const int prevColor = (GetImageColor(*imageToDraw, mouseX, mouseY).r < 5)? 0 : 1;
+                
                 ImageDrawPixel(imageToDraw, mouseX, mouseY, (firstColor) ? BLACK : RAYWHITE);
-                if (prevColor != firstColor)
-                    UpdateTextureRec(currentWorld->texture, (Rectangle){ floorf(offsetX), floorf(offsetY), (float)(sizeInWorldX), (float)(sizeInWorldY) }, imageToDraw->data);
+                
+                if (prevColor != firstColor) UpdateTextureRec(currentWorld->texture, (Rectangle){ floorf(offsetX), floorf(offsetY), (float)(sizeInWorldX), (float)(sizeInWorldY) }, imageToDraw->data);
             }
-            else
-                firstColor = -1;
+            else firstColor = -1;
         }
 
         // Load selected preset
-        //----------------------------------------------------------------------------------
         if (preset >= 0)
         {
             Image pattern;
             if (preset < numberOfPresets - 1)   // Preset with pattern image lo load
             {
                 pattern = LoadImage(TextFormat("resources/game_of_life/%s.png", presetPatterns[preset].fileName));
+                
                 BeginTextureMode(*currentWorld);
                     ClearBackground(RAYWHITE);
                 EndTextureMode();
+                
                 UpdateTextureRec(currentWorld->texture, (Rectangle){ worldWidth*presetPatterns[preset].position.x - pattern.width/2.0f,
                                                                      worldHeight*presetPatterns[preset].position.y - pattern.height/2.0f,
                                                                      (float)(pattern.width), (float)(pattern.height) }, pattern.data);
@@ -240,9 +233,12 @@ int main(void)
                     {
                         ImageClearBackground(&pattern, RAYWHITE);
                         for (int x = 0; x < pattern.width; x++)
+                        {
                             for (int y = 0; y < pattern.height; y++)
-                                if (GetRandomValue(0, 100) < 15)
-                                    ImageDrawPixel(&pattern, x, y, BLACK);
+                            {
+                                if (GetRandomValue(0, 100) < 15) ImageDrawPixel(&pattern, x, y, BLACK);
+                            }
+                        }
                         UpdateTextureRec(currentWorld->texture,
                                          (Rectangle){ (float)(pattern.width*i), (float)(pattern.height*j),
                                                       (float)(pattern.width), (float)(pattern.height) }, pattern.data);
@@ -251,26 +247,25 @@ int main(void)
             }
 
             UnloadImage(pattern);
+            
             mode = MODE_PAUSE;
-            offsetX = worldWidth * presetPatterns[preset].position.x - windowWidth/zoom/2.0f;
-            offsetY = worldHeight * presetPatterns[preset].position.y - windowHeight/zoom/2.0f;
+            offsetX = worldWidth*presetPatterns[preset].position.x - windowWidth/zoom/2.0f;
+            offsetY = worldHeight*presetPatterns[preset].position.y - windowHeight/zoom/2.0f;
         }
 
         // Check window draw inside world limits
         if (offsetX < 0) offsetX = 0;
         if (offsetY < 0) offsetY = 0;
-        if (offsetX > worldWidth - (float)(windowWidth)/zoom)
-            offsetX = worldWidth - (float)(windowWidth)/zoom;
-        if (offsetY > worldHeight - (float)(windowHeight)/zoom)
-            offsetY = worldHeight - (float)(windowHeight)/zoom;
+        if (offsetX > worldWidth - (float)(windowWidth)/zoom) offsetX = worldWidth - (float)(windowWidth)/zoom;
+        if (offsetY > worldHeight - (float)(windowHeight)/zoom) offsetY = worldHeight - (float)(windowHeight)/zoom;
 
         // Rectangles for drawing texture portion to screen
-        //----------------------------------------------------------------------------------
         const Rectangle textureSourceToScreen = { offsetX, offsetY, (float)windowWidth/zoom, (float)windowHeight/zoom };
+        //----------------------------------------------------------------------------------
 
         // Draw to texture
         //----------------------------------------------------------------------------------
-        if ((mode == MODE_RUN) && ((frame % framesPerStep) == 0))
+        if ((mode == MODE_RUN) && ((frame%framesPerStep) == 0))
         {
             // Swap worlds
             RenderTexture2D *tempWorld = currentWorld;
@@ -284,10 +279,12 @@ int main(void)
                 EndShaderMode();
             EndTextureMode();
         }
+        //----------------------------------------------------------------------------------
 
         // Draw to screen
         //----------------------------------------------------------------------------------
         BeginDrawing();
+        
             DrawTexturePro(currentWorld->texture, textureSourceToScreen, textureOnScreen, (Vector2){ 0, 0 }, 0.0f, WHITE);
 
             DrawLine(windowWidth, 0, windowWidth, screenHeight, (Color){ 218, 218, 218, 255 });
@@ -301,8 +298,7 @@ int main(void)
             DrawText("Presets", 710, 58, 8, GRAY);
             preset = -1;
             for (int i = 0; i < numberOfPresets; i++)
-                if (GuiButton((Rectangle){ 710.0f, 70.0f + 18*i, 80.0f, 16.0f }, presetPatterns[i].name))
-                    preset = i;
+                if (GuiButton((Rectangle){ 710.0f, 70.0f + 18*i, 80.0f, 16.0f }, presetPatterns[i].name)) preset = i;
 
             GuiToggleGroup((Rectangle){ 710, 258, 80, 16 }, "Run\nPause\nDraw", &mode);
 
@@ -314,8 +310,6 @@ int main(void)
             buttonFaster = GuiButton((Rectangle){ 710, 382, 80, 16 }, "Faster");
             buttonSlower = GuiButton((Rectangle){ 710, 400, 80, 16 }, "Slower");
 
-            //------------------------------------------------------------------------------
-
             DrawFPS(712, 426);
 
         EndDrawing();

src/rcore.c

@@ -1743,7 +1743,32 @@ int GetRandomValue(int min, int max)
         TRACELOG(LOG_WARNING, "Invalid GetRandomValue() arguments, range should not be higher than %i", RAND_MAX);
     }
     
-    value = (rand()%(abs(max - min) + 1) + min);
+    // NOTE: This one-line approach produces a non-uniform distribution,
+    // as stated by Donald Knuth in the book The Art of Programming, so
+    // using below approach for more uniform results
+    //value = (rand()%(abs(max - min) + 1) + min);
+
+    // More uniform range solution
+    int range = (max - min) + 1;
+
+    // Degenerate/overflow case: fall back to min (same behavior as "always min" instead of UB)
+    if (range <= 0) value = min;
+    else
+    {
+        // Rejection sampling to get a uniform integer in [min, max]
+        unsigned long c = (unsigned long)RAND_MAX + 1UL;  // number of possible rand() results
+        unsigned long m = (unsigned long)range;           // size of the target interval
+        unsigned long t = c - (c%m);                    // largest multiple of m <= c
+        unsigned long r = 0;
+
+        for (;;)
+        {
+            r = (unsigned long)rand();
+            if (r < t) break;   // Only accept values within the fair region
+        }
+
+        value = min + (int)(r%m);
+    }
 #endif
     return value;
 }

src/rlgl.h

@@ -3384,10 +3384,12 @@ unsigned int rlLoadTexture(const void *data, int width, int height, int format,
 #if defined(GRAPHICS_API_OPENGL_33)
     if (mipmapCount > 1)
     {
-        // Activate Trilinear filtering if mipmaps are available
+        // Activate trilinear filtering if mipmaps are available
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
-        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, mipmapCount); // Required for user-defined mip count
+        
+        // Define thee maximum number of mipmap levels to be used, 0 is default texture size
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, mipmapCount - 1);
     }
 #endif