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196 lines
5.4 KiB
196 lines
5.4 KiB
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short-description: A simple GUI tutorial |
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... |
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# Building a simple SDL2 app from scratch |
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This page shows from the ground up how to define and build an SDL2 gui |
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application using nothing but Meson. The document is written for |
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Windows, as it is the most complex platform, but the same basic ideas |
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should work on Linux and macOS as well. |
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The sample application is written in plain C as SDL 2 is also written |
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in C. If you prefer C++ instead, the conversion is fairly simple and |
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is left as an exercise to the reader. |
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This document assumes that you have already installed both Visual |
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Studio and Meson. |
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# Set up the build directory |
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First you need to create an empty directory for all your stuff. The |
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Visual Studio toolchain is a bit unusual in that it requires you to |
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run your builds from a specific shell. This can be found by opening |
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the application menu and then choosing `Visual Studio <year> -> x86_64 |
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native tools command prompt`. |
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It will put you in a weird directory, so you need to go to your home |
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directory: |
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cd \users\yourusername |
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Typically you'd type `cd \users\` and then press the tabulator key to |
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make the shell autocomplete the username. Once that is done you can |
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create the directory. |
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mkdir sdldemo |
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cd sdldemo |
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# Creating the sample program |
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Now we need to create a source file and a Meson build definition file. |
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We're not going to use SDL at all, but instead start with a simple |
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program that only prints some text. Once we have it working we can |
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extend it to do graphics. The source goes into a file `sdlprog.c` and |
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has the following contents: |
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```c |
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#include <stdio.h> |
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int main(int argc, char **argv) { |
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printf("App is running.\n"); |
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return 0; |
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} |
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``` |
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The build definition goes to a file called `meson.build` and looks |
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like this: |
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```meson |
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project('sdldemo', 'c') |
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executable('sdlprog', 'sdlprog.c') |
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``` |
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With this done we can start the build with the following command: |
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meson setup builddir |
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Here `builddir` is the _build directory_, everything that is generated |
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during the build is put in that directory. When run, it should look |
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like this. |
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![Configuring the sample application](images/sdltutorial_01.png) |
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The program is compiled with this: |
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meson compile -C builddir |
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The `-C` argument tells Meson where the configured build directory is. |
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The program will be in the build directory and can be run like this: |
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builddir\sdlprog |
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The output should look like this. |
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![Running the sample application](images/sdltutorial_02.png) |
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# Upgrading the program to use SDL |
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The code needed to start SDL is a bit more complicated and we're not |
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going to go into how it works. Merely replace the contents of |
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`sdlprog.c` with the following: |
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```c |
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#include "SDL.h" |
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int main(int argc, char *argv[]) |
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{ |
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SDL_Window *window; |
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SDL_Renderer *renderer; |
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SDL_Surface *surface; |
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SDL_Event event; |
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if (SDL_Init(SDL_INIT_VIDEO) < 0) { |
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SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't initialize SDL: %s", SDL_GetError()); |
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return 3; |
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} |
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if (SDL_CreateWindowAndRenderer(320, 240, SDL_WINDOW_RESIZABLE, &window, &renderer)) { |
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SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't create window and renderer: %s", SDL_GetError()); |
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return 3; |
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} |
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while (1) { |
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SDL_PollEvent(&event); |
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if (event.type == SDL_QUIT) { |
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break; |
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} |
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SDL_SetRenderDrawColor(renderer, 0x00, 0x00, 0x00, 0x00); |
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SDL_RenderClear(renderer); |
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SDL_RenderPresent(renderer); |
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} |
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SDL_DestroyRenderer(renderer); |
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SDL_DestroyWindow(window); |
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SDL_Quit(); |
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return 0; |
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} |
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``` |
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Let's try to compile this by running `meson compile -C builddir` again. |
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![Building SDL app fails](images/sdltutorial_03.png) |
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That fails. The reason for this is that we don't actually have SDL |
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currently available. We need to obtain it somehow. In more technical |
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terms SDL2 is an _external dependency_ and obtaining it is called |
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_dependency resolution_. |
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Meson has a web service for downloading and building (if needed) |
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dependencies called a WrapDB. It provides SDL2 so we can use it |
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directly. First we need to create a `subprojects` directory because in |
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Meson all subprojects like these must be stored in that directory for |
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consistency. |
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mkdir subprojects |
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Then we can install the dependency: |
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meson wrap install sdl2 |
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It looks like this: |
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![Obtaining SDL2 from WrapDB](images/sdltutorial_04.png) |
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As a final step we need to update our build definition file to use the |
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newly obtained dependency. |
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```meson |
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project('sdldemo', 'c', |
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default_options: 'default_library=static') |
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sdl2_dep = dependency('sdl2') |
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executable('sdlprog', 'sdlprog.c', |
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win_subsystem: 'windows', |
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dependencies: sdl2_dep) |
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``` |
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In addition to the dependency this has a few other changes. First we |
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specify that we want to build helper libraries statically. For simple |
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projects like these it makes things simpler. We also need to tell |
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Meson that the program we are building is a Windows GUI |
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application rather than a console application. |
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This is all we need to do and can now run `meson compile` again. First |
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the system downloads and configures SDL2: |
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![Running the sample application](images/sdltutorial_05.png) |
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A bit later the compilation exits successfully. |
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![Running the sample application](images/sdltutorial_06.png) |
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# Program is done |
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Now we can run the application with |
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builddir\sdlprog |
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The end result is a black SDL window. |
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![Running the sample application](images/sdltutorial_07.png)
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