examples: added renderer/04-points

examples/CMakeLists.txt

@@ -123,6 +123,7 @@ endmacro()
 add_sdl_example_executable(renderer-clear SOURCES renderer/01-clear/renderer-clear.c)
 add_sdl_example_executable(renderer-primitives SOURCES renderer/02-primitives/renderer-primitives.c)
 add_sdl_example_executable(renderer-lines SOURCES renderer/03-lines/renderer-lines.c)
+add_sdl_example_executable(renderer-points SOURCES renderer/04-points/renderer-points.c)
 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/02-primitives/README.txt

@@ -1,3 +1,7 @@
 This example creates an SDL window and renderer, and then draws some lines,
 rectangles and points to it every frame.
 
+This is just a quick overview of simple drawing primitives; futher examples
+will explore them in more detail.
+
+

examples/renderer/03-lines/renderer-lines.c

@@ -56,7 +56,7 @@ SDL_AppResult SDL_AppIterate(void *appstate)
     };
 
     /* as you can see from this, rendering draws over whatever was drawn before it. */
-    SDL_SetRenderDrawColor(renderer, 100, 100, 100, 255);  /* black, full alpha */
+    SDL_SetRenderDrawColor(renderer, 100, 100, 100, 255);  /* grey, full alpha */
     SDL_RenderClear(renderer);  /* start with a blank canvas. */
 
     /* You can draw lines, one at a time, like these brown ones... */

examples/renderer/04-points/README.txt

@@ -0,0 +1,3 @@
+This example creates an SDL window and renderer, and then draws a bunch of
+single points, moving across the screen.
+

examples/renderer/04-points/renderer-points.c

@@ -0,0 +1,118 @@
+/*
+ * This example creates an SDL window and renderer, and then draws some points
+ * to it every frame.
+ *
+ * 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>
+
+/* We will use this renderer to draw into this window every frame. */
+static SDL_Window *window = NULL;
+static SDL_Renderer *renderer = NULL;
+static Uint64 last_time = 0;
+
+#define WINDOW_WIDTH 640
+#define WINDOW_HEIGHT 480
+
+#define NUM_POINTS 500
+#define MIN_PIXELS_PER_SECOND 30  /* move at least this many pixels per second. */
+#define MAX_PIXELS_PER_SECOND 60  /* move this many pixels per second at most. */
+
+/* (track everything as parallel arrays instead of a array of structs,
+   so we can pass the coordinates to the renderer in a single function call.) */
+
+/* Points are plotted as a set of X and Y coordinates.
+   (0, 0) is the top left of the window, and larger numbers go down
+   and to the right. This isn't how geometry works, but this is pretty
+   standard in 2D graphics. */
+static SDL_FPoint points[NUM_POINTS];
+static float point_speeds[NUM_POINTS];
+
+/* This function runs once at startup. */
+SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
+{
+    int i;
+
+    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/points", WINDOW_WIDTH, WINDOW_HEIGHT, 0, &window, &renderer)) {
+        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create window/renderer!", SDL_GetError(), NULL);
+        return SDL_APP_FAILURE;
+    }
+
+    SDL_srand(0);  /* seed the random number generator */
+
+    /* set up the data for a bunch of points. */
+    for (i = 0; i < SDL_arraysize(points); i++) {
+        points[i].x = SDL_randf() * ((float) WINDOW_WIDTH);
+        points[i].y = SDL_randf() * ((float) WINDOW_HEIGHT);
+        point_speeds[i] = MIN_PIXELS_PER_SECOND + (SDL_randf() * (MAX_PIXELS_PER_SECOND - MIN_PIXELS_PER_SECOND));
+    }
+
+    last_time = SDL_GetTicks();
+
+    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 Uint64 now = SDL_GetTicks();
+    const float elapsed = ((float) (now - last_time)) / 1000.0f;  /* seconds since last iteration */
+    int i;
+
+    /* let's move all our points a little for a new frame. */
+    for (i = 0; i < SDL_arraysize(points); i++) {
+        const float distance = elapsed * point_speeds[i];
+        points[i].x += distance;
+        points[i].y += distance;
+        if ((points[i].x >= WINDOW_WIDTH) || (points[i].y >= WINDOW_HEIGHT)) {
+            /* off the screen; restart it elsewhere! */
+            if (SDL_rand(2)) {
+                points[i].x = SDL_randf() * ((float) WINDOW_WIDTH);
+                points[i].y = 0.0f;
+            } else {
+                points[i].x = 0.0f;
+                points[i].y = SDL_randf() * ((float) WINDOW_HEIGHT);
+            }
+            point_speeds[i] = MIN_PIXELS_PER_SECOND + (SDL_randf() * (MAX_PIXELS_PER_SECOND - MIN_PIXELS_PER_SECOND));
+        }
+    }
+
+    last_time = now;
+
+    /* as you can see from this, rendering draws over whatever was drawn before it. */
+    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);  /* black, full alpha */
+    SDL_RenderClear(renderer);  /* start with a blank canvas. */
+    SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);  /* white, full alpha */
+    SDL_RenderPoints(renderer, points, SDL_arraysize(points));  /* draw all the points! */
+
+    /* You can also draw single points with SDL_RenderPoint(), but it's
+       cheaper (sometimes significantly so) to do them all at once. */
+
+    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 will clean up the window/renderer for us. */
+}
+