Atlas - cliprect.c
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[FILE BEGIN]
1/*
2 * This example creates an SDL window and renderer, and then draws a scene
3 * to it every frame, while sliding around a clipping rectangle.
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#define WINDOW_WIDTH 640
13#define WINDOW_HEIGHT 480
14#define CLIPRECT_SIZE 250
15#define CLIPRECT_SPEED 200   /* pixels per second */
16
17/* We will use this renderer to draw into this window every frame. */
18static SDL_Window *window = NULL;
19static SDL_Renderer *renderer = NULL;
20static SDL_Texture *texture = NULL;
21static SDL_FPoint cliprect_position;
22static SDL_FPoint cliprect_direction;
23static Uint64 last_time = 0;
24
25/* A lot of this program is examples/renderer/02-primitives, so we have a good
26   visual that we can slide a clip rect around. The actual new magic in here
27   is the SDL_SetRenderClipRect() function. */
28
29/* This function runs once at startup. */
30SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
31{
32    SDL_Surface *surface = NULL;
33    char *png_path = NULL;
34
35    SDL_SetAppMetadata("Example Renderer Clipping Rectangle", "1.0", "com.example.renderer-cliprect");
36
37    if (!SDL_Init(SDL_INIT_VIDEO)) {
38        SDL_Log("Couldn't initialize SDL: %s", SDL_GetError());
39        return SDL_APP_FAILURE;
40    }
41
42    if (!SDL_CreateWindowAndRenderer("examples/renderer/cliprect", WINDOW_WIDTH, WINDOW_HEIGHT, SDL_WINDOW_RESIZABLE, &window, &renderer)) {
43        SDL_Log("Couldn't create window/renderer: %s", SDL_GetError());
44        return SDL_APP_FAILURE;
45    }
46    SDL_SetRenderLogicalPresentation(renderer, WINDOW_WIDTH, WINDOW_HEIGHT, SDL_LOGICAL_PRESENTATION_LETTERBOX);
47
48    cliprect_direction.x = cliprect_direction.y = 1.0f;
49
50    last_time = SDL_GetTicks();
51
52    /* Textures are pixel data that we upload to the video hardware for fast drawing. Lots of 2D
53       engines refer to these as "sprites." We'll do a static texture (upload once, draw many
54       times) with data from a bitmap file. */
55
56    /* SDL_Surface is pixel data the CPU can access. SDL_Texture is pixel data the GPU can access.
57       Load a .png into a surface, move it to a texture from there. */
58    SDL_asprintf(&png_path, "%ssample.png", SDL_GetBasePath());  /* allocate a string of the full file path */
59    surface = SDL_LoadPNG(png_path);
60    if (!surface) {
61        SDL_Log("Couldn't load bitmap: %s", SDL_GetError());
62        return SDL_APP_FAILURE;
63    }
64
65    SDL_free(png_path);  /* done with this, the file is loaded. */
66
67    texture = SDL_CreateTextureFromSurface(renderer, surface);
68    if (!texture) {
69        SDL_Log("Couldn't create static texture: %s", SDL_GetError());
70        return SDL_APP_FAILURE;
71    }
72
73    SDL_DestroySurface(surface);  /* done with this, the texture has a copy of the pixels now. */
74
75    return SDL_APP_CONTINUE;  /* carry on with the program! */
76}
77
78/* This function runs when a new event (mouse input, keypresses, etc) occurs. */
79SDL_AppResult SDL_AppEvent(void *appstate, SDL_Event *event)
80{
81    if (event->type == SDL_EVENT_QUIT) {
82        return SDL_APP_SUCCESS;  /* end the program, reporting success to the OS. */
83    }
84    return SDL_APP_CONTINUE;  /* carry on with the program! */
85}
86
87/* This function runs once per frame, and is the heart of the program. */
88SDL_AppResult SDL_AppIterate(void *appstate)
89{
90    const SDL_Rect cliprect = { (int) SDL_roundf(cliprect_position.x), (int) SDL_roundf(cliprect_position.y), CLIPRECT_SIZE, CLIPRECT_SIZE };
91    const Uint64 now = SDL_GetTicks();
92    const float elapsed = ((float) (now - last_time)) / 1000.0f;  /* seconds since last iteration */
93    const float distance = elapsed * CLIPRECT_SPEED;
94
95    /* Set a new clipping rectangle position */
96    cliprect_position.x += distance * cliprect_direction.x;
97    if (cliprect_position.x < -CLIPRECT_SIZE) {
98        cliprect_position.x = -CLIPRECT_SIZE;
99        cliprect_direction.x = 1.0f;
100    } else if (cliprect_position.x >= WINDOW_WIDTH) {
101        cliprect_position.x = WINDOW_WIDTH - 1;
102        cliprect_direction.x = -1.0f;
103    }
104
105    cliprect_position.y += distance * cliprect_direction.y;
106    if (cliprect_position.y < -CLIPRECT_SIZE) {
107        cliprect_position.y = -CLIPRECT_SIZE;
108        cliprect_direction.y = 1.0f;
109    } else if (cliprect_position.y >= WINDOW_HEIGHT) {
110        cliprect_position.y = WINDOW_HEIGHT - 1;
111        cliprect_direction.y = -1.0f;
112    }
113    SDL_SetRenderClipRect(renderer, &cliprect);
114
115    last_time = now;
116
117    /* okay, now draw! */
118
119    /* Note that SDL_RenderClear is _not_ affected by the clipping rectangle! */
120    SDL_SetRenderDrawColor(renderer, 33, 33, 33, SDL_ALPHA_OPAQUE);  /* grey, full alpha */
121    SDL_RenderClear(renderer);  /* start with a blank canvas. */
122
123    /* stretch the texture across the entire window. Only the piece in the
124       clipping rectangle will actually render, though! */
125    SDL_RenderTexture(renderer, texture, NULL, NULL);
126
127    SDL_RenderPresent(renderer);  /* put it all on the screen! */
128
129    return SDL_APP_CONTINUE;  /* carry on with the program! */
130}
131
132/* This function runs once at shutdown. */
133void SDL_AppQuit(void *appstate, SDL_AppResult result)
134{
135    SDL_DestroyTexture(texture);
136    /* SDL will clean up the window/renderer for us. */
137}
138
139
[FILE END]
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