Added no_std_rendering example.

examples/no_std_rendering.rs

@@ -0,0 +1,112 @@
+// all of this code in the run() function works in a no_std environment
+// feel free to split this example into main.rs and lib.rs files
+
+//#![no_std]
+
+use fermium::prelude::*;
+
+struct ProgramState {
+    done: bool,
+    hue: f32,
+    hue_shift_speed: f32,
+}
+
+// start main.rs
+// use fermium_no_std_rendering::run;
+
+fn main() {
+  run();
+}
+// end main.rs
+
+#[no_mangle]
+pub extern "C" fn run() {
+    let mut ps = ProgramState {
+        done: false,
+        hue: 0.0,
+        hue_shift_speed: 0.001,
+    };
+
+    unsafe { assert_eq!(SDL_Init(SDL_INIT_EVERYTHING), 0) };
+    let window = unsafe {
+        SDL_CreateWindow(
+            b"Fermium no_std Hue Shift Rendering Demo\0".as_ptr().cast(),
+            SDL_WINDOWPOS_CENTERED,
+            SDL_WINDOWPOS_CENTERED,
+            800,
+            600,
+            (SDL_WINDOW_OPENGL | SDL_WINDOW_ALLOW_HIGHDPI).0,
+        )
+    };
+    assert!(!window.is_null());
+
+    let default_driver = -1;
+    let renderer =
+        unsafe { SDL_CreateRenderer(window, default_driver, SDL_RENDERER_ACCELERATED.0) };
+    assert!(!renderer.is_null());
+
+    while !ps.done {
+        update(&mut ps);
+        render(renderer, &ps);
+    }
+    unsafe { SDL_Quit() };
+}
+
+fn update(ps: &mut ProgramState) {
+    // handle quitting
+    let mut event = SDL_Event::default();
+    let pending_events = 0 < unsafe { SDL_PollEvent(&mut event) };
+    if pending_events {
+        let event_type = unsafe { event.type_ };
+        if event_type == SDL_QUIT || event_type == SDL_KEYDOWN {
+            ps.done = true
+        }
+    }
+
+    // handle hue animation
+    ps.hue += ps.hue_shift_speed;
+    ps.hue %= 1.0;
+}
+
+fn render(renderer: *mut SDL_Renderer, ps: &ProgramState) {
+    // calculate values for hue to RGB conversion
+    let chroma = 1.0;
+    let h_prime = ps.hue * 6.0;
+    // no no_std abs(), so this variable is defined
+    // (h_prime % 2.0 - 1.0).abs()
+    let hue_shifted = if 1.0 < h_prime % 2.0 {
+        h_prime % 2.0 - 1.0
+    } else {
+        1.0 - h_prime % 2.0
+    };
+    let x = chroma * (1.0 - hue_shifted);
+
+    // get RGB components
+    let (r, g, b) = if h_prime < 1.0 {
+        (chroma, x, 0.0)
+    } else if h_prime < 2.0 {
+        (x, chroma, 0.0)
+    } else if h_prime < 3.0 {
+        (0.0, chroma, x)
+    } else if h_prime < 4.0 {
+        (0.0, x, chroma)
+    } else if h_prime < 5.0 {
+        (x, 0.0, chroma)
+    } else {
+        (chroma, 0.0, x)
+    };
+
+    // set window color
+    unsafe {
+        SDL_SetRenderDrawColor(
+            renderer,
+            (r * 255.0) as u8,
+            (g * 255.0) as u8,
+            (b * 255.0) as u8,
+            255,
+        );
+        SDL_RenderClear(renderer);
+        SDL_RenderPresent(renderer);
+    }
+}
+