Playing with tiled triangles in different shades of grey.

moartriangles.c

#include "SDL.h"
#include "SDL_gfxPrimitives.h"
#include "SDL_framerate.h"

#include <stdbool.h>
#include <math.h>

static const int laycnt = 7;
static int layalpha[7];
static double lay[7];

void
draw_triangles( SDL_Surface *surface, int x1, int y1, int x2, int y2, int tri_width, int tri_height ) {
    int i, sx, sy;

    i = 0;
    sy = y1 - tri_height;
    while( sy < y2 ) {
        sx = x1 - tri_width;
        while( sx <= x2 ) {
            int middle_point_x = sx + (tri_width / 2);
            int lcorner_x = sx;

            if( i % 2 == 0 ) {
                /* Point at bottom */
                int middle_point_y = sy + ((tri_height / 3));
                int lcorner_y = sy;
                int rcorner_x = sx + tri_width;
                int rcorner_y = sy;
                int pcorner_y = sy + tri_height;

                filledTrigonRGBA(surface,
                    lcorner_x, lcorner_y,
                    rcorner_x, rcorner_y,
                    middle_point_x, middle_point_y,
                    255, 255, 255, layalpha[1]);

                filledTrigonRGBA(surface,
                    lcorner_x, lcorner_y,
                    middle_point_x, middle_point_y,
                    middle_point_x, pcorner_y,
                    255, 255, 255, layalpha[2]);

                filledTrigonRGBA(surface,
                    rcorner_x, rcorner_y,
                    middle_point_x, middle_point_y,
                    middle_point_x, pcorner_y,
                    255, 255, 255, layalpha[3]);
            }
            else {
                /* Point at top */
                int middle_point_y = sy + ((tri_height / 3) * 2);
                int lcorner_y = sy + tri_height;
                int rcorner_x = sx + tri_width;
                int rcorner_y = sy + tri_height;
                int pcorner_y = sy;

                filledTrigonRGBA(surface,
                    lcorner_x, lcorner_y,
                    rcorner_x, rcorner_y,
                    middle_point_x, middle_point_y,
                    255, 255, 255, layalpha[4]);

                filledTrigonRGBA(surface,
                    lcorner_x, lcorner_y,
                    middle_point_x, middle_point_y,
                    middle_point_x, pcorner_y,
                    255, 255, 255, layalpha[5]);

                filledTrigonRGBA(surface,
                    rcorner_x, rcorner_y,
                    middle_point_x, middle_point_y,
                    middle_point_x, pcorner_y,
                    255, 255, 255, layalpha[6]);
            }

            i++;
            sx += (tri_width / 2);
        }
        sy += tri_height;
    }
}

#define WINDOW_WIDTH 1280
#define WINDOW_HEIGHT 720

int
main( int argc, char **argv ) {
    int i;
    SDL_Init( SDL_INIT_VIDEO );
    SDL_Surface *screen = SDL_SetVideoMode( WINDOW_WIDTH, WINDOW_HEIGHT, 0, SDL_HWSURFACE | SDL_DOUBLEBUF );
    SDL_WM_SetCaption( "Moar Triangles", 0 );

    SDL_Event event;
    FPSmanager framerate;
    bool is_running = true;

    for( i = 0; i < laycnt; i++ ) {
        lay[i] = 0;
    }

    SDL_initFramerate(&framerate);
    SDL_setFramerate(&framerate, 30);

    while( is_running ) {
        if( SDL_PollEvent(&event) ) {
            if( event.type == SDL_QUIT ) {
                is_running = false;
            }
            else if( event.type == SDL_KEYDOWN ) {
                if( event.key.keysym.sym == SDLK_ESCAPE ) {
                    is_running = false;
                }
            }
        }

        for( i = 0; i < laycnt; i++ ) {
            lay[i] += i;
            layalpha[i] = 50 + fabs(sin(1 + (lay[i] / 300))) * 200;
        }

        SDL_FillRect( screen, NULL, SDL_MapRGB(screen->format, 0, 0, 0) );

        draw_triangles(screen, 0, 0, WINDOW_WIDTH, WINDOW_HEIGHT, 60, 40);

        SDL_Flip( screen );

        SDL_framerateDelay(&framerate);
    }

    SDL_Quit();

    return 0;
}

It creates many interesting geometric patterns