add null backend

src/framework/backend.rs

@@ -51,7 +51,13 @@ pub trait BackendTexture {
 }
 
 pub fn init_backend() -> GameResult<Box<dyn Backend>> {
-    crate::framework::backend_sdl2::SDL2Backend::new()
+    #[cfg(feature = "backend_sdl")]
+        {
+            return crate::framework::backend_sdl2::SDL2Backend::new()
+        }
+
+    log::warn!("No backend compiled in, using null backend instead.");
+    crate::framework::backend_null::NullBackend::new()
 }
 
 pub enum SpriteBatchCommand {

src/framework/backend_null.rs

@@ -0,0 +1,125 @@
+use crate::framework::backend::{Backend, BackendEventLoop, BackendRenderer, BackendTexture, SpriteBatchCommand};
+use crate::framework::error::GameResult;
+use crate::framework::context::Context;
+use crate::Game;
+use crate::common::{Rect, Color};
+use imgui::{Ui, DrawData};
+use crate::framework::graphics::BlendMode;
+use std::cell::RefCell;
+use std::ops::DerefMut;
+use std::mem;
+
+pub struct NullBackend;
+
+impl NullBackend {
+    pub fn new() -> GameResult<Box<dyn Backend>> {
+        Ok(Box::new(NullBackend))
+    }
+}
+
+impl Backend for NullBackend {
+    fn create_event_loop(&self) -> GameResult<Box<dyn BackendEventLoop>> {
+        Ok(Box::new(NullEventLoop))
+    }
+}
+
+pub struct NullEventLoop;
+
+impl BackendEventLoop for NullEventLoop {
+    fn run(&mut self, game: &mut Game, ctx: &mut Context) {
+        let state_ref = unsafe { &mut *game.state.get() };
+
+        loop {
+            game.update(ctx).unwrap();
+            if state_ref.shutdown {
+                log::info!("Shutting down...");
+                break;
+            }
+            if state_ref.next_scene.is_some() {
+                mem::swap(&mut game.scene, &mut state_ref.next_scene);
+                state_ref.next_scene = None;
+                game.scene.as_mut().unwrap().init(state_ref, ctx).unwrap();
+                game.loops = 0;
+                state_ref.frame_time = 0.0;
+            }
+            std::thread::sleep(std::time::Duration::from_millis(10));
+            game.draw(ctx).unwrap();
+        }
+    }
+
+    fn new_renderer(&self) -> GameResult<Box<dyn BackendRenderer>> {
+        let mut imgui = imgui::Context::create();
+        imgui.io_mut().display_size = [640.0, 480.0];
+        imgui.fonts().build_alpha8_texture();
+
+        Ok(Box::new(NullRenderer(RefCell::new(imgui))))
+    }
+}
+
+pub struct NullTexture(u16, u16);
+
+impl BackendTexture for NullTexture {
+    fn dimensions(&self) -> (u16, u16) {
+        (self.0, self.1)
+    }
+
+    fn add(&mut self, command: SpriteBatchCommand) {
+
+    }
+
+    fn clear(&mut self) {
+
+    }
+
+    fn draw(&mut self) -> GameResult<()> {
+        Ok(())
+    }
+}
+
+pub struct NullRenderer(RefCell<imgui::Context>);
+
+impl BackendRenderer for NullRenderer {
+    fn clear(&mut self, color: Color) {
+
+    }
+
+    fn present(&mut self) -> GameResult {
+        Ok(())
+    }
+
+    fn create_texture_mutable(&mut self, width: u16, height: u16) -> GameResult<Box<dyn BackendTexture>> {
+        Ok(Box::new(NullTexture(width, height)))
+    }
+
+    fn create_texture(&mut self, width: u16, height: u16, data: &[u8]) -> GameResult<Box<dyn BackendTexture>> {
+        Ok(Box::new(NullTexture(width, height)))
+    }
+
+    fn set_blend_mode(&mut self, blend: BlendMode) -> GameResult {
+        Ok(())
+    }
+
+    fn set_render_target(&mut self, texture: Option<&Box<dyn BackendTexture>>) -> GameResult {
+        Ok(())
+    }
+
+    fn draw_rect(&mut self, rect: Rect<isize>, color: Color) -> GameResult {
+        Ok(())
+    }
+
+    fn draw_outline_rect(&mut self, rect: Rect<isize>, line_width: usize, color: Color) -> GameResult {
+        Ok(())
+    }
+
+    fn imgui(&self) -> GameResult<&mut imgui::Context> {
+        unsafe { Ok(&mut *self.0.as_ptr()) }
+    }
+
+    fn render_imgui(&mut self, draw_data: &DrawData) -> GameResult {
+        Ok(())
+    }
+
+    fn prepare_frame<'ui>(&self, ui: &Ui<'ui>) -> GameResult {
+        Ok(())
+    }
+}

src/framework/mod.rs

@@ -1,4 +1,5 @@
 pub mod backend;
+#[cfg(feature = "backend_sdl2")]
 pub mod backend_sdl2;
 pub mod backend_null;
 pub mod context;