examples: Added renderer/15-cliprect

examples/CMakeLists.txt

@@ -132,6 +132,7 @@ add_sdl_example_executable(renderer-scaling-textures SOURCES renderer/09-scaling
 add_sdl_example_executable(renderer-geometry SOURCES renderer/10-geometry/geometry.c DATAFILES ${CMAKE_CURRENT_SOURCE_DIR}/../test/sample.bmp)
 add_sdl_example_executable(renderer-color-mods SOURCES renderer/11-color-mods/color-mods.c DATAFILES ${CMAKE_CURRENT_SOURCE_DIR}/../test/sample.bmp)
 add_sdl_example_executable(renderer-viewport SOURCES renderer/14-viewport/viewport.c DATAFILES ${CMAKE_CURRENT_SOURCE_DIR}/../test/sample.bmp)
+add_sdl_example_executable(renderer-cliprect SOURCES renderer/15-cliprect/cliprect.c DATAFILES ${CMAKE_CURRENT_SOURCE_DIR}/../test/sample.bmp)
 add_sdl_example_executable(audio-simple-playback SOURCES audio/01-simple-playback/simple-playback.c)
 add_sdl_example_executable(audio-simple-playback-callback SOURCES audio/02-simple-playback-callback/simple-playback-callback.c)
 add_sdl_example_executable(audio-load-wav SOURCES audio/03-load-wav/load-wav.c DATAFILES ${CMAKE_CURRENT_SOURCE_DIR}/../test/sample.wav)

examples/renderer/15-cliprect/README.txt

@@ -0,0 +1,5 @@
+This example creates an SDL window and renderer, loads a texture
+from a .bmp file, and stretches it across the window. Each frame, we move
+the clipping rectangle around, so only a small square of the texture is
+actually drawn.
+

examples/renderer/15-cliprect/cliprect.c

@@ -0,0 +1,135 @@
+/*
+ * This example creates an SDL window and renderer, and then draws a scene
+ * to it every frame, while sliding around a clipping rectangle.
+ *
+ * This code is public domain. Feel free to use it for any purpose!
+ */
+
+#define SDL_MAIN_USE_CALLBACKS 1  /* use the callbacks instead of main() */
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_main.h>
+
+#define WINDOW_WIDTH 640
+#define WINDOW_HEIGHT 480
+#define CLIPRECT_SIZE 250
+#define CLIPRECT_SPEED 200   /* pixels per second */
+
+/* We will use this renderer to draw into this window every frame. */
+static SDL_Window *window = NULL;
+static SDL_Renderer *renderer = NULL;
+static SDL_Texture *texture = NULL;
+static SDL_FPoint cliprect_position;
+static SDL_FPoint cliprect_direction;
+static Uint64 last_time = 0;
+
+/* A lot of this program is examples/renderer/02-primitives, so we have a good
+   visual that we can slide a clip rect around. The actual new magic in here
+   is the SDL_SetRenderClipRect() function. */
+
+/* This function runs once at startup. */
+SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
+{
+    SDL_Surface *surface = NULL;
+    char *bmp_path = NULL;
+
+    if (!SDL_Init(SDL_INIT_VIDEO)) {
+        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't initialize SDL!", SDL_GetError(), NULL);
+        return SDL_APP_FAILURE;
+    }
+
+    if (!SDL_CreateWindowAndRenderer("examples/renderer/primitives", WINDOW_WIDTH, WINDOW_HEIGHT, 0, &window, &renderer)) {
+        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create window/renderer!", SDL_GetError(), NULL);
+        return SDL_APP_FAILURE;
+    }
+
+    cliprect_direction.x = cliprect_direction.y = 1.0f;
+
+    last_time = SDL_GetTicks();
+
+    /* Textures are pixel data that we upload to the video hardware for fast drawing. Lots of 2D
+       engines refer to these as "sprites." We'll do a static texture (upload once, draw many
+       times) with data from a bitmap file. */
+
+    /* SDL_Surface is pixel data the CPU can access. SDL_Texture is pixel data the GPU can access.
+       Load a .bmp into a surface, move it to a texture from there. */
+    SDL_asprintf(&bmp_path, "%ssample.bmp", SDL_GetBasePath());  /* allocate a string of the full file path */
+    surface = SDL_LoadBMP(bmp_path);
+    if (!surface) {
+        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't load bitmap!", SDL_GetError(), NULL);
+        return SDL_APP_FAILURE;
+    }
+
+    SDL_free(bmp_path);  /* done with this, the file is loaded. */
+
+    texture = SDL_CreateTextureFromSurface(renderer, surface);
+    if (!texture) {
+        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create static texture!", SDL_GetError(), NULL);
+        return SDL_APP_FAILURE;
+    }
+
+    SDL_DestroySurface(surface);  /* done with this, the texture has a copy of the pixels now. */
+
+    return SDL_APP_CONTINUE;  /* carry on with the program! */
+}
+
+/* This function runs when a new event (mouse input, keypresses, etc) occurs. */
+SDL_AppResult SDL_AppEvent(void *appstate, SDL_Event *event)
+{
+    if (event->type == SDL_EVENT_QUIT) {
+        return SDL_APP_SUCCESS;  /* end the program, reporting success to the OS. */
+    }
+    return SDL_APP_CONTINUE;  /* carry on with the program! */
+}
+
+/* This function runs once per frame, and is the heart of the program. */
+SDL_AppResult SDL_AppIterate(void *appstate)
+{
+    const SDL_Rect cliprect = { (int) SDL_roundf(cliprect_position.x), (int) SDL_roundf(cliprect_position.y), CLIPRECT_SIZE, CLIPRECT_SIZE };
+    const Uint64 now = SDL_GetTicks();
+    const float elapsed = ((float) (now - last_time)) / 1000.0f;  /* seconds since last iteration */
+    const float distance = elapsed * CLIPRECT_SPEED;
+
+    /* Set a new clipping rectangle position */
+    cliprect_position.x += distance * cliprect_direction.x;
+    if (cliprect_position.x < 0.0f) {
+        cliprect_position.x = 0.0f;
+        cliprect_direction.x = 1.0f;
+    } else if (cliprect_position.x >= (WINDOW_WIDTH - CLIPRECT_SIZE)) {
+        cliprect_position.x = (WINDOW_WIDTH - CLIPRECT_SIZE) - 1;
+        cliprect_direction.x = -1.0f;
+    }
+
+    cliprect_position.y += distance * cliprect_direction.y;
+    if (cliprect_position.y < 0.0f) {
+        cliprect_position.y = 0.0f;
+        cliprect_direction.y = 1.0f;
+    } else if (cliprect_position.y >= (WINDOW_HEIGHT - CLIPRECT_SIZE)) {
+        cliprect_position.y = (WINDOW_HEIGHT - CLIPRECT_SIZE) - 1;
+        cliprect_direction.y = -1.0f;
+    }
+    SDL_SetRenderClipRect(renderer, &cliprect);
+
+    last_time = now;
+
+    /* okay, now draw! */
+
+    /* Note that SDL_RenderClear is _not_ affected by the clipping rectangle! */
+    SDL_SetRenderDrawColor(renderer, 33, 33, 33, 255);  /* grey, full alpha */
+    SDL_RenderClear(renderer);  /* start with a blank canvas. */
+
+    /* stretch the texture across the entire window. Only the piece in the
+       clipping rectangle will actually render, though! */
+    SDL_RenderTexture(renderer, texture, NULL, NULL);
+
+    SDL_RenderPresent(renderer);  /* put it all on the screen! */
+
+    return SDL_APP_CONTINUE;  /* carry on with the program! */
+}
+
+/* This function runs once at shutdown. */
+void SDL_AppQuit(void *appstate)
+{
+    SDL_DestroyTexture(texture);
+    /* SDL will clean up the window/renderer for us. */
+}
+