From 6140f567ba1ad4cacb5fdc99e0d7807b29a4190b Mon Sep 17 00:00:00 2001 From: "Ryan C. Gordon" Date: Mon, 12 Aug 2024 00:25:10 -0400 Subject: [PATCH] examples: added a basic pen example. --- examples/CMakeLists.txt | 1 + examples/pen/01-pen-drawing-lines/README.txt | 3 + .../01-pen-drawing-lines/pen-drawing-lines.c | 104 ++++++++++++++++++ 3 files changed, 108 insertions(+) create mode 100644 examples/pen/01-pen-drawing-lines/README.txt create mode 100644 examples/pen/01-pen-drawing-lines/pen-drawing-lines.c diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt index 298596feda..36a80721b3 100644 --- a/examples/CMakeLists.txt +++ b/examples/CMakeLists.txt @@ -186,6 +186,7 @@ add_sdl_example_executable(renderer-primitives SOURCES renderer/02-primitives/re 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) +add_sdl_example_executable(pen-drawing-lines SOURCES pen/01-pen-drawing-lines/pen-drawing-lines.c) add_sdl_example_executable(game-snake SOURCES game/01-snake/main.c game/01-snake/snake.c) diff --git a/examples/pen/01-pen-drawing-lines/README.txt b/examples/pen/01-pen-drawing-lines/README.txt new file mode 100644 index 0000000000..693cda8f28 --- /dev/null +++ b/examples/pen/01-pen-drawing-lines/README.txt @@ -0,0 +1,3 @@ +You need something with a pen/stylus for this to work. + +This takes pen input and draws lines. Lines are darker when you press harder. diff --git a/examples/pen/01-pen-drawing-lines/pen-drawing-lines.c b/examples/pen/01-pen-drawing-lines/pen-drawing-lines.c new file mode 100644 index 0000000000..ef9aa6e6b2 --- /dev/null +++ b/examples/pen/01-pen-drawing-lines/pen-drawing-lines.c @@ -0,0 +1,104 @@ +/* + * This example code reads pen/stylus input and draws lines. Darker lines + * for harder pressure. + * + * SDL can track multiple pens, but for simplicity here, this assumes any + * pen input we see was from one device. + * + * 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 +#include + +/* 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 *render_target = NULL; +static float pressure = 0.0f; +static float previous_touch_x = -1.0f; +static float previous_touch_y = -1.0f; + +/* This function runs once at startup. */ +int SDL_AppInit(void **appstate, int argc, char *argv[]) +{ + if (SDL_Init(SDL_INIT_VIDEO) == -1) { + SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't initialize SDL!", SDL_GetError(), NULL); + return SDL_APP_FAILURE; + } + + if (SDL_CreateWindowAndRenderer("examples/pen/drawing-lines", 640, 480, 0, &window, &renderer) == -1) { + SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create window/renderer!", SDL_GetError(), NULL); + return SDL_APP_FAILURE; + } + + /* we make a render target so we can draw lines to it and not have to record and redraw every pen stroke each frame. + Instead rendering a frame for us is a single texture draw. */ + render_target = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET, 640, 480); + if (!render_target) { + SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create render target!", SDL_GetError(), NULL); + return SDL_APP_FAILURE; + } + + /* just blank the render target to gray to start. */ + SDL_SetRenderTarget(renderer, render_target); + SDL_SetRenderDrawColor(renderer, 100, 100, 100, 255); + SDL_RenderClear(renderer); + SDL_SetRenderTarget(renderer, NULL); + SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND); + + return SDL_APP_CONTINUE; /* carry on with the program! */ +} + +/* This function runs when a new event (mouse input, keypresses, etc) occurs. */ +int SDL_AppEvent(void *appstate, const SDL_Event *event) +{ + if (event->type == SDL_EVENT_QUIT) { + return SDL_APP_SUCCESS; /* end the program, reporting success to the OS. */ + } + + /* There are several events that track the specific stages of pen activity, + but we're only going to look for motion and pressure, for simplicity. */ + if (event->type == SDL_EVENT_PEN_MOTION) { + /* you can check for when the pen is touching, but if pressure > 0.0f, it's definitely touching! */ + if (pressure > 0.0f) { + if (previous_touch_x >= 0.0f) { /* only draw if we're moving while touching */ + /* draw with the alpha set to the pressure, so you effectively get a fainter line for lighter presses. */ + SDL_SetRenderTarget(renderer, render_target); + SDL_SetRenderDrawColorFloat(renderer, 0, 0, 0, pressure); + SDL_RenderLine(renderer, previous_touch_x, previous_touch_y, event->pmotion.x, event->pmotion.y); + } + previous_touch_x = event->pmotion.x; + previous_touch_y = event->pmotion.y; + } else { + previous_touch_x = previous_touch_y = -1.0f; + } + } else if (event->type == SDL_EVENT_PEN_AXIS) { + if (event->paxis.axis == SDL_PEN_AXIS_PRESSURE) { + pressure = event->paxis.value; /* remember new pressure for later draws. */ + } + } + + return SDL_APP_CONTINUE; /* carry on with the program! */ +} + +/* This function runs once per frame, and is the heart of the program. */ +int SDL_AppIterate(void *appstate) +{ + /* make sure we're drawing to the window and not the render target */ + SDL_SetRenderTarget(renderer, NULL); + SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255); + SDL_RenderClear(renderer); /* just in case. */ + SDL_RenderTexture(renderer, render_target, NULL, NULL); + SDL_RenderPresent(renderer); + return SDL_APP_CONTINUE; /* carry on with the program! */ +} + +/* This function runs once at shutdown. */ +void SDL_AppQuit(void *appstate) +{ + SDL_DestroyTexture(render_target); + /* SDL will clean up the window/renderer for us. */ +} +