new example: shaders_eratosthenes

Contributed by ProfJski

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;
+}