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July 7, 2024 05:57
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Janet SDL Example
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| # This is an example of how to use SDL in Janet using the FFI module. | |
| # This is based on Lazy Foo's tutorial that can be found at: | |
| # https://lazyfoo.net/tutorials/SDL/01_hello_SDL/index2.php | |
| # | |
| # In order to run this, you need: | |
| # - To have libSDL2.so at the same folder where the source code is. | |
| # - Create three separate files, as descibed by the comments below. | |
| # - Read the FFI docs here: | |
| # https://janet-lang.org/1.25.1/docs/ffi.html | |
| # | |
| # Some Notes: | |
| # - Source code has been tested in Linux only. | |
| # - I code in Clojure, this is my very first code written in Janet. | |
| # It may not be idiomatic or following the language's conventions. | |
| # | |
| # In case you are not able to see the screen, run with -r and it will | |
| # start the repl while the screen is running. | |
| # File: hello-sdl.janet --- | |
| #!/usr/bin/env janet | |
| # Here we import the files which contain the FFI, contants and idiomatic api. | |
| (import ./sdl :as sdl) | |
| (import ./sdl-janet :as sdlj) | |
| # Initializes SDL. Here we use some constants from the sdl module. | |
| (sdlj/sdl-init! (get sdl/sdl-constants :sdl/sdl-init-video)) | |
| # This let block will create the window and paint a surface. | |
| (let [screen-size [640 480] | |
| background-color [255 255 255] | |
| {:window/window window | |
| :window/window-surface window-surface} (sdlj/sdl-create-window "SDL Tutorial" 0 0 ;screen-size) | |
| pixel-format (get window-surface :surface/sdl-pixel-format) | |
| fill-color (sdlj/sdl-map-rgb pixel-format ;background-color)] | |
| (sdlj/sdl-fill-rect! (get window-surface :ptr) nil fill-color)) | |
| # File: sdl.janet --- | |
| # This will load the SDL library into the FFI context. | |
| (ffi/context "./libSDL2.so") | |
| # Those constants have been copied from SDL's source code. | |
| (def sdl-constants {:sdl/sdl-init-video 0x00000020 | |
| :sdl/sdl-window-shown 0x00000004}) | |
| # Defines the struct for the SDL surface. | |
| (def SDL_Surface (ffi/struct :uint32 :ptr :int :int :ptr :ptr :int :ptr :ptr :ptr :int)) | |
| # We use defbind to create a binding to the C function. | |
| # We can replace _ by - so it matches the lisp convention. | |
| (ffi/defbind SDL-Init :uint32 [init-video :uint32]) | |
| # You can find a list of all avilable types in the FFI link mentioned above. | |
| (ffi/defbind SDL-CreateWindow :ptr | |
| [title :string | |
| x :int | |
| y :int | |
| w :int | |
| h :int | |
| flags :uint32]) | |
| (ffi/defbind SDL-GetWindowSurface :ptr [window :ptr]) | |
| (ffi/defbind SDL-UpdateWindowSurface :int [window :ptr]) | |
| (ffi/defbind SDL-FillRect :int | |
| [surface :ptr | |
| sdl-rect :ptr | |
| color :uint32]) | |
| (ffi/defbind SDL-MapRGB :uint32 | |
| [format :ptr | |
| r :uint8 | |
| g :uint8 | |
| b :uint8]) | |
| # File: sdl-janet.janet --- | |
| # Import the SDL file listed above. | |
| (import ./sdl :as sdl) | |
| # We access FFI structs by the index of the field in the struct. | |
| # This is quite annoying, and it makes sense to create a mapped struct in which | |
| # you can access fields using get and get-in. | |
| # It receives a pointer to the FFI struct... | |
| (defn make-sdl-surface | |
| [ffi-ptr] | |
| # ... and we read it to a buffer using the declared struct from the sdl module. | |
| (let [surface (ffi/read sdl/SDL_Surface ffi-ptr)] | |
| # Now that we have the buffer, we can access the values. | |
| {:surface/ptr ffi-ptr | |
| :surface/flags (get surface 0) | |
| :surface/sdl-pixel-format (get surface 1) | |
| :surface/w (get surface 2) | |
| :surface/height (get surface 3) | |
| :surface/pitch (get surface 4) | |
| :surface/pixels (get surface 5) | |
| :surface/userdata (get surface 6) | |
| :surface/locked (get surface 7) | |
| :surface/lock-data (get surface 8) | |
| :surface/clip-rect (get surface 9) | |
| :surface/sdl-blitmap (get surface 10) | |
| :surface/refcount(get surface 11)})) | |
| (defn- make-sdl-window | |
| [window] | |
| (let [surface (sdl/SDL-GetWindowSurface window)] | |
| {:window/window window | |
| :window/window-surface (make-sdl-surface surface)})) | |
| (defn sdl-init! | |
| [flags] | |
| (let [processes-flags flags | |
| status (sdl/SDL-Init flags)] | |
| (when (< status 0) | |
| # !!! | |
| # I am not sure if this is the correct way of throwing an error. | |
| # Do not use this as a reference. | |
| # !!! | |
| (error :sdl-janet-error/sdl-init-video)))) | |
| (defn sdl-create-window | |
| [title pos-x pos-y width height] | |
| (let [flags (get sdl/sdl-constants :sdl/sdl-window-shown) | |
| window (sdl/SDL-CreateWindow title pos-x pos-y width height flags)] | |
| (when (nil? window) | |
| (error :sdl-janet-error/create-window)) | |
| (make-sdl-window window))) | |
| (defn sdl-map-rgb | |
| [pixel-format r g b] | |
| (sdl/SDL-MapRGB pixel-format r g b)) | |
| (defn sdl-fill-rect! | |
| [surface rect color] | |
| (sdl/SDL-FillRect surface rect color)) |
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