Atlas - points.c
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[FILE BEGIN]
1/*
2 * This example creates an SDL window and renderer, and then draws some points
3 * to it every frame.
4 *
5 * This code is public domain. Feel free to use it for any purpose!
6 */
7
8#define SDL_MAIN_USE_CALLBACKS 1  /* use the callbacks instead of main() */
9#include <SDL3/SDL.h>
10#include <SDL3/SDL_main.h>
11
12/* We will use this renderer to draw into this window every frame. */
13static SDL_Window *window = NULL;
14static SDL_Renderer *renderer = NULL;
15static Uint64 last_time = 0;
16
17#define WINDOW_WIDTH 640
18#define WINDOW_HEIGHT 480
19
20#define NUM_POINTS 500
21#define MIN_PIXELS_PER_SECOND 30  /* move at least this many pixels per second. */
22#define MAX_PIXELS_PER_SECOND 60  /* move this many pixels per second at most. */
23
24/* (track everything as parallel arrays instead of a array of structs,
25   so we can pass the coordinates to the renderer in a single function call.) */
26
27/* Points are plotted as a set of X and Y coordinates.
28   (0, 0) is the top left of the window, and larger numbers go down
29   and to the right. This isn't how geometry works, but this is pretty
30   standard in 2D graphics. */
31static SDL_FPoint points[NUM_POINTS];
32static float point_speeds[NUM_POINTS];
33
34/* This function runs once at startup. */
35SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
36{
37    int i;
38
39    SDL_SetAppMetadata("Example Renderer Points", "1.0", "com.example.renderer-points");
40
41    if (!SDL_Init(SDL_INIT_VIDEO)) {
42        SDL_Log("Couldn't initialize SDL: %s", SDL_GetError());
43        return SDL_APP_FAILURE;
44    }
45
46    if (!SDL_CreateWindowAndRenderer("examples/renderer/points", WINDOW_WIDTH, WINDOW_HEIGHT, SDL_WINDOW_RESIZABLE, &window, &renderer)) {
47        SDL_Log("Couldn't create window/renderer: %s", SDL_GetError());
48        return SDL_APP_FAILURE;
49    }
50    SDL_SetRenderLogicalPresentation(renderer, WINDOW_WIDTH, WINDOW_HEIGHT, SDL_LOGICAL_PRESENTATION_LETTERBOX);
51
52    /* set up the data for a bunch of points. */
53    for (i = 0; i < SDL_arraysize(points); i++) {
54        points[i].x = SDL_randf() * ((float) WINDOW_WIDTH);
55        points[i].y = SDL_randf() * ((float) WINDOW_HEIGHT);
56        point_speeds[i] = MIN_PIXELS_PER_SECOND + (SDL_randf() * (MAX_PIXELS_PER_SECOND - MIN_PIXELS_PER_SECOND));
57    }
58
59    last_time = SDL_GetTicks();
60
61    return SDL_APP_CONTINUE;  /* carry on with the program! */
62}
63
64/* This function runs when a new event (mouse input, keypresses, etc) occurs. */
65SDL_AppResult SDL_AppEvent(void *appstate, SDL_Event *event)
66{
67    if (event->type == SDL_EVENT_QUIT) {
68        return SDL_APP_SUCCESS;  /* end the program, reporting success to the OS. */
69    }
70    return SDL_APP_CONTINUE;  /* carry on with the program! */
71}
72
73/* This function runs once per frame, and is the heart of the program. */
74SDL_AppResult SDL_AppIterate(void *appstate)
75{
76    const Uint64 now = SDL_GetTicks();
77    const float elapsed = ((float) (now - last_time)) / 1000.0f;  /* seconds since last iteration */
78    int i;
79
80    /* let's move all our points a little for a new frame. */
81    for (i = 0; i < SDL_arraysize(points); i++) {
82        const float distance = elapsed * point_speeds[i];
83        points[i].x += distance;
84        points[i].y += distance;
85        if ((points[i].x >= WINDOW_WIDTH) || (points[i].y >= WINDOW_HEIGHT)) {
86            /* off the screen; restart it elsewhere! */
87            if (SDL_rand(2)) {
88                points[i].x = SDL_randf() * ((float) WINDOW_WIDTH);
89                points[i].y = 0.0f;
90            } else {
91                points[i].x = 0.0f;
92                points[i].y = SDL_randf() * ((float) WINDOW_HEIGHT);
93            }
94            point_speeds[i] = MIN_PIXELS_PER_SECOND + (SDL_randf() * (MAX_PIXELS_PER_SECOND - MIN_PIXELS_PER_SECOND));
95        }
96    }
97
98    last_time = now;
99
100    /* as you can see from this, rendering draws over whatever was drawn before it. */
101    SDL_SetRenderDrawColor(renderer, 0, 0, 0, SDL_ALPHA_OPAQUE);  /* black, full alpha */
102    SDL_RenderClear(renderer);  /* start with a blank canvas. */
103    SDL_SetRenderDrawColor(renderer, 255, 255, 255, SDL_ALPHA_OPAQUE);  /* white, full alpha */
104    SDL_RenderPoints(renderer, points, SDL_arraysize(points));  /* draw all the points! */
105
106    /* You can also draw single points with SDL_RenderPoint(), but it's
107       cheaper (sometimes significantly so) to do them all at once. */
108
109    SDL_RenderPresent(renderer);  /* put it all on the screen! */
110
111    return SDL_APP_CONTINUE;  /* carry on with the program! */
112}
113
114/* This function runs once at shutdown. */
115void SDL_AppQuit(void *appstate, SDL_AppResult result)
116{
117    /* SDL will clean up the window/renderer for us. */
118}
119
120
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