most basic sand sim you can create with Raylib 4.0

.sand.c.md

most basic sand sim you can create with Raylib 4.0

main.c

#include <stdlib.h>
#include "raylib.h"
#include "math.h"
#include "rlgl.h"

bool SameRGB ( Color lhs , Color rhs );
bool SwapIf ( Color condition , int src , Color srcColor , int dst , char tick , Color* pixels );

#define AIR SKYBLUE
#define SAND ORANGE
#define WATER BLUE
const int screenWidth = 640;
const int screenHeight = 480;
const int pixelScale = 10;
const int pixelsWidth = screenWidth / pixelScale;
const int pixelsHeight = screenHeight / pixelScale;
const int pixelsLength = pixelsWidth * pixelsHeight;

int main ( void )
{
    // Initialization
    InitWindow( screenWidth , screenHeight , "sand" );
    SetTargetFPS( 30 );

    // NOTE: Textures MUST be loaded after Window initialization (OpenGL context is required)

    // Dynamic memory allocation to store pixels data (Color type)
    Color *pixels = (Color*) malloc( pixelsLength * sizeof(Color) );
    for( int i=0 ; i<pixelsLength ; i++ ) pixels[i] = AIR;

    // Load pixels data into an image structure and create texture
    Image pixelsImage = {
        .data = pixels,
        .width = pixelsWidth,
        .height = pixelsHeight,
        .format = PIXELFORMAT_UNCOMPRESSED_R8G8B8A8,
        .mipmaps = 1
    };

    Texture2D pixelsTexture = LoadTextureFromImage( pixelsImage );
    SetTextureFilter( pixelsTexture , TEXTURE_FILTER_POINT );

    // GAME LOOP
    unsigned char tick = 0;
    while( !WindowShouldClose() )
    {
        // UPDATE
        float dt = GetFrameTime();
        double time = GetTime();
        tick++;
        Vector2 mouse = GetMousePosition();
        int mouseX = (int) mouse.x;
        int mouseY = (int) mouse.y;
        int mousePixelIndex = mouseY/pixelScale * pixelsWidth + mouseX/pixelScale;
        {
            for( int y=0 ; y<pixelsHeight ; y++ )
            for( int x=0 ; x<pixelsWidth ; x++ )
            {
                int src = y*pixelsWidth + x;
                Color srcColor = pixels[src];

                if( SameRGB(srcColor,AIR) ) continue;// early exit

                int down = (y+1)*pixelsWidth + x;
                int downRight = (y+1)*pixelsWidth + x+1;
                int downLeft = (y+1)*pixelsWidth + x-1;
                int right = y*pixelsWidth + x+1;
                int left = y*pixelsWidth + x-1;

                if( SameRGB(srcColor,SAND) && srcColor.a!=tick )// is this SAND && not changed this frame
                {
                    // falling down
                    if( SwapIf(AIR,src,srcColor,down,tick,pixels) ) continue;
                    else if( SwapIf(WATER,src,srcColor,down,tick,pixels ) ) continue;

                    if( GetRandomValue(0,1)==1 )
                    if( SwapIf(AIR,src,srcColor,downRight,tick,pixels) ) continue;
                    else if( SwapIf(WATER,src,srcColor,downRight,tick,pixels ) ) continue;
                    
                    if( GetRandomValue(0,1)==1 )
                    if( SwapIf(AIR,src,srcColor,downLeft,tick,pixels) ) continue;
                    else if( SwapIf(WATER,src,srcColor,downLeft,tick,pixels ) ) continue;
                }
                else if( SameRGB(srcColor,WATER) && srcColor.a!=tick )// is this WATER && not changed this frame
                {
                    // falling down
                    if( SwapIf(AIR,src,srcColor,down,tick,pixels) ) continue;

                    if( GetRandomValue(0,1)==1 )
                    if( SwapIf(AIR,src,srcColor,downRight,tick,pixels) ) continue;
                    
                    if( GetRandomValue(0,1)==1 )
                    if( SwapIf(AIR,src,srcColor,downLeft,tick,pixels) ) continue;
                    
                    // moving sideways
                    if( GetRandomValue(0,1)==1 )
                    if( SwapIf(AIR,src,srcColor,right,tick,pixels) ) continue;
                    
                    if( GetRandomValue(0,1)==1 )
                    if( SwapIf(AIR,src,srcColor,left,tick,pixels) ) continue;
                }
            }

            if( IsMouseButtonDown(0) )
            {
                pixels[mousePixelIndex] = SAND;
                pixels[mousePixelIndex].a = tick;
            }
            else if( IsMouseButtonDown(1) )
            {
                pixels[mousePixelIndex] = WATER;
                pixels[mousePixelIndex].a = tick;
            }
            else if( IsMouseButtonDown(2) )
            {
                pixels[mousePixelIndex] = AIR;
                pixels[mousePixelIndex].a = tick;
            }
        }

        // RENDER
        BeginDrawing();
        {
            // ClearBackground( BLACK );
            rlSetBlendFactors( 1 , 0 , 0x0104 );// 1 for GL_ONE, 0 for GL_ZERO, 0x0104 for GL_ADD
            rlSetBlendMode( BLEND_CUSTOM );
            UpdateTexture( pixelsTexture , pixels );
            DrawTextureEx( pixelsTexture , (Vector2){ 0 , 0 } , 0 , pixelScale , WHITE );
            // DrawText( TextFormat( "mouse:(%i,%i)" , mouseX , mouseY ), 72, 148, 30, BLUE );
        }
        EndDrawing();
    }

    // De-Initialization
    UnloadImage( pixelsImage );// unloads CPU (RAM) image data (pixels)
    UnloadTexture( pixelsTexture );
    CloseWindow();// Close window and OpenGL context
    return 0;
}

bool SameRGB ( Color lhs , Color rhs ) { return lhs.r==rhs.r && lhs.g==rhs.g && lhs.b==rhs.b; }

bool SwapIf ( Color condition , int src , Color srcColor , int dst , char tick , Color* pixels )
{
    if( dst>=0 && dst<pixelsLength )
    {
        Color dstColor = pixels[dst];
        if( dstColor.a!=tick )// not changed this frame
        if( SameRGB(dstColor,condition) )
        {
            pixels[dst] = srcColor;
            pixels[dst].a = tick;

            pixels[src] = dstColor;
            pixels[src].a = tick;

            return true;
        }
    }
    return false;
}