raylib-src/examples/shaders/shaders_eratosthenes.c

/*******************************************************************************************
*
*   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(void)
{
    // 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);               // Set our game to run at 60 frames-per-second
    //--------------------------------------------------------------------------------------

    // 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;
}