new example: shaders_eratosthenes

Contributed by ProfJski

examples/Makefile

@@ -451,6 +451,7 @@ EXAMPLES = \
     shaders/shaders_texture_drawing \
     shaders/shaders_texture_waves \
     shaders/shaders_julia_set \
+    shaders/shaders_eratosthenes \
     audio/audio_module_playing \
     audio/audio_music_stream \
     audio/audio_raw_stream \

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

@@ -0,0 +1,58 @@
+#version 100
+
+precision mediump float;
+
+/*************************************************************************************
+
+  The Sieve of Eratosthenes -- a simple shader by ProfJski
+  An early prime number sieve: https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+
+  The screen is divided into a square grid of boxes, each representing an integer value.
+  Each integer is tested to see if it is a prime number.  Primes are colored white.
+  Non-primes are colored with a color that indicates the smallest factor which evenly divdes our integer.
+
+  You can change the scale variable to make a larger or smaller grid.  
+  Total number of integers displayed = scale squared, so scale = 100 tests the first 10,000 integers.
+
+  WARNING: If you make scale too large, your GPU may bog down!
+
+***************************************************************************************/
+
+// Input vertex attributes (from vertex shader)
+varying vec2 fragTexCoord;
+varying vec4 fragColor;
+
+// Make a nice spectrum of colors based on counter and maxSize
+vec4 Colorizer(float counter, float maxSize)
+{
+    float red = 0.0, green = 0.0, blue = 0.0;
+    float normsize = counter/maxSize;
+    
+    red = smoothstep(0.3, 0.7, normsize);
+    green = sin(3.14159*normsize);
+    blue = 1.0 - smoothstep(0.0, 0.4, normsize);
+    
+    return vec4(0.8*red, 0.8*green, 0.8*blue, 1.0);
+}
+
+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
+    {
+        for (int i = 2; (i < max(2, sqrt(value) + 1)); i++) 
+        {
+            if ((value - i*floor(value/i)) == 0) 
+            {
+                color = Colorizer(float(i), scale);
+                //break;    // Uncomment to color by the largest factor instead
+            }
+        }
+
+        gl_FragColor = color;
+    }
+}

examples/shaders/resources/shaders/glsl330/eratosthenes.fs

@@ -0,0 +1,59 @@
+#version 330
+
+/*************************************************************************************
+
+  The Sieve of Eratosthenes -- a simple shader by ProfJski
+  An early prime number sieve: https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+
+  The screen is divided into a square grid of boxes, each representing an integer value.
+  Each integer is tested to see if it is a prime number.  Primes are colored white.
+  Non-primes are colored with a color that indicates the smallest factor which evenly divdes our integer.
+
+  You can change the scale variable to make a larger or smaller grid.  
+  Total number of integers displayed = scale squared, so scale = 100 tests the first 10,000 integers.
+
+  WARNING: If you make scale too large, your GPU may bog down!
+
+***************************************************************************************/
+
+// Input vertex attributes (from vertex shader)
+in vec2 fragTexCoord;
+in vec4 fragColor;
+
+// Output fragment color
+out vec4 finalColor;
+
+// Make a nice spectrum of colors based on counter and maxSize
+vec4 Colorizer(float counter, float maxSize)
+{
+    float red = 0.0, green = 0.0, blue = 0.0;
+    float normsize = counter/maxSize;
+    
+    red = smoothstep(0.3, 0.7, normsize);
+    green = sin(3.14159*normsize);
+    blue = 1.0 - smoothstep(0.0, 0.4, normsize);
+    
+    return vec4(0.8*red, 0.8*green, 0.8*blue, 1.0);
+}
+
+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)) finalColor = vec4(1.0);
+    else
+    {
+        for (int i = 2; (i < max(2, sqrt(value) + 1)); i++) 
+        {
+            if ((value - i*floor(value/i)) == 0) 
+            {
+                color = Colorizer(float(i), scale);
+                //break;    // Uncomment to color by the largest factor instead
+            }
+        }
+
+        finalColor = color;
+    }
+}

examples/shaders/shaders_eratosthenes.c

@@ -0,0 +1,94 @@
+/*******************************************************************************************
+*
+*   raylib [shaders] example - Sieve of Eratosthenes
+*
+*   Sieve of Eratosthenes, the earliest known (ancient Greek) prime number sieve.
+*
+*   "Sift the twos and sift the threes,
+*    The Sieve of Eratosthenes.
+*    When the multiples sublime,
+*    the numbers that are left are prime."
+*
+*   NOTE: This example requires raylib OpenGL 3.3 or ES2 versions for shaders support,
+*         OpenGL 1.1 does not support shaders, recompile raylib to OpenGL 3.3 version.
+*
+*   NOTE: Shaders used in this example are #version 330 (OpenGL 3.3).
+*
+*   This example has been created using raylib 2.5 (www.raylib.com)
+*   raylib is licensed under an unmodified zlib/libpng license (View raylib.h for details)
+*
+*   Example contributed by ProfJski and reviewed by Ramon Santamaria (@raysan5)
+*
+*   Copyright (c) 2019 ProfJski and Ramon Santamaria (@raysan5)
+*
+********************************************************************************************/
+
+#include "raylib.h"
+
+#if defined(PLATFORM_DESKTOP)
+    #define GLSL_VERSION            330
+#else   // PLATFORM_RPI, PLATFORM_ANDROID, PLATFORM_WEB
+    #define GLSL_VERSION            100
+#endif
+
+int main()
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const int screenWidth = 800;
+    const int screenHeight = 450;
+
+    InitWindow(screenWidth, screenHeight, "raylib [shaders] example - Sieve of Eratosthenes");
+
+    RenderTexture2D target = LoadRenderTexture(screenWidth, screenHeight);
+    
+    // Load Eratosthenes shader
+    // NOTE: Defining 0 (NULL) for vertex shader forces usage of internal default vertex shader
+    Shader shader = LoadShader(0, FormatText("resources/shaders/glsl%i/eratosthenes.fs", GLSL_VERSION));
+
+    SetTargetFPS(60);
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!WindowShouldClose())                // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        // Nothing to do here, everything is happening in the shader
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+            ClearBackground(RAYWHITE);
+
+            BeginTextureMode(target);   // Enable drawing to texture
+                ClearBackground(BLACK);     // Clear the render texture
+
+                // 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);
+            EndTextureMode();           // End drawing to texture (now we have a blank texture available for the shader)
+
+            BeginShaderMode(shader);
+                // NOTE: Render texture must be y-flipped due to default OpenGL coordinates (left-bottom)
+                DrawTextureRec(target.texture, (Rectangle){ 0, 0, target.texture.width, -target.texture.height }, (Vector2){ 0.0f, 0.0f }, WHITE);
+            EndShaderMode();
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    UnloadShader(shader);           // Unload shader
+    UnloadRenderTexture(target);    // Unload texture
+
+    CloseWindow();                  // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+
+    return 0;
+}