examples: Avoid dividing index to get x, y; calculate index from x, y

examples/animation.rs

@@ -78,10 +78,11 @@ fn pre_render_frames(width: usize, height: usize) -> Vec<Vec<u32>> {
     let render = |frame_id| {
         let elapsed = ((frame_id as f64) / (60.0)) * 2.0 * PI;
 
-        (0..(width * height))
-            .map(|index| {
-                let y = ((index / width) as f64) / (height as f64);
-                let x = ((index % width) as f64) / (width as f64);
+        let coords = (0..height).flat_map(|x| (0..width).map(move |y| (x, y)));
+        coords
+            .map(|(x, y)| {
+                let y = (y as f64) / (height as f64);
+                let x = (x as f64) / (width as f64);
                 let red =
                     ((((y + elapsed).sin() * 0.5 + 0.5) * 255.0).round() as u32).clamp(0, 255);
                 let green =

examples/rectangle.rs

@@ -4,17 +4,17 @@ use winit::event_loop::{ControlFlow, EventLoop};
 use winit::window::WindowBuilder;
 
 fn redraw(buffer: &mut [u32], width: usize, height: usize, flag: bool) {
-    for (index, color) in buffer.iter_mut().enumerate() {
-        let y = index / width;
-        let x = index % width;
-
-        if flag && x >= 100 && x < width - 100 && y >= 100 && y < height - 100 {
-            *color = 0x00ffffff;
-        } else {
-            let red = (x & 0xff) ^ (y & 0xff);
-            let green = (x & 0x7f) ^ (y & 0x7f);
-            let blue = (x & 0x3f) ^ (y & 0x3f);
-            *color = (blue | (green << 8) | (red << 16)) as u32;
+    for y in 0..height {
+        for x in 0..width {
+            let value = if flag && x >= 100 && x < width - 100 && y >= 100 && y < height - 100 {
+                0x00ffffff
+            } else {
+                let red = (x & 0xff) ^ (y & 0xff);
+                let green = (x & 0x7f) ^ (y & 0x7f);
+                let blue = (x & 0x3f) ^ (y & 0x3f);
+                (blue | (green << 8) | (red << 16)) as u32
+            };
+            buffer[y * width + x] = value;
         }
     }
 }

examples/winit.rs

@@ -42,14 +42,14 @@ fn main() {
                     .unwrap();
 
                 let mut buffer = surface.buffer_mut().unwrap();
-                for index in 0..(width * height) {
-                    let y = index / width;
-                    let x = index % width;
-                    let red = x % 255;
-                    let green = y % 255;
-                    let blue = (x * y) % 255;
-
-                    buffer[index as usize] = blue | (green << 8) | (red << 16);
+                for y in 0..height {
+                    for x in 0..width {
+                        let red = x % 255;
+                        let green = y % 255;
+                        let blue = (x * y) % 255;
+                        let index = y as usize * width as usize + x as usize;
+                        buffer[index] = blue | (green << 8) | (red << 16);
+                    }
                 }
 
                 buffer.present().unwrap();