Validate width and height inputs (#162)

* Validate width and height inputs

- Fixes #157

* Add window size check to `imgui-winit` demo

- There is really nothing better that can be done in this case.
- The surface, buffer, and world sizes must all be non-zero.
- A zero-length surface would (previously) panic in `wgpu`.
- A zero-length buffer would panic with the new assertions.
- A zero-length world would cause a divide-by-zero panic when drawing.

examples/imgui-winit/src/main.rs

@@ -100,13 +100,15 @@ fn main() -> Result<(), Error> {
 
             // Resize the window
             if let Some(size) = input.window_resized() {
-                // Resize the surface texture
-                pixels.resize_surface(size.width, size.height);
+                if size.width > 0 && size.height > 0 {
+                    // Resize the surface texture
+                    pixels.resize_surface(size.width, size.height);
 
-                // Resize the world
-                let LogicalSize { width, height } = size.to_logical(scale_factor);
-                world.resize(width, height);
-                pixels.resize_buffer(width, height);
+                    // Resize the world
+                    let LogicalSize { width, height } = size.to_logical(scale_factor);
+                    world.resize(width, height);
+                    pixels.resize_buffer(width, height);
+                }
             }
 
             // Update internal state and request a redraw

src/lib.rs

@@ -203,7 +203,14 @@ impl Pixels {
     ///
     /// Call this method to change the virtual screen resolution. E.g. when you want your pixel
     /// buffer to be resized from `640x480` to `800x600`.
+    ///
+    /// # Panics
+    ///
+    /// Panics when `width` or `height` are 0.
     pub fn resize_buffer(&mut self, width: u32, height: u32) {
+        assert!(width > 0);
+        assert!(height > 0);
+
         // Recreate the backing texture
         let (scaling_matrix_inverse, texture_extent, texture, scaling_renderer, pixels_buffer_size) =
             builder::create_backing_texture(
@@ -237,8 +244,12 @@ impl Pixels {
     /// texture for non-integer scaling ratios.
     ///
     /// Call this method in response to a resize event from your window manager. The size expected
-    /// is in physical pixel units.
+    /// is in physical pixel units. Does nothing when `width` or `height` are 0.
     pub fn resize_surface(&mut self, width: u32, height: u32) {
+        if width == 0 || height == 0 {
+            return;
+        }
+
         // Update SurfaceTexture dimensions
         self.surface_size.width = width;
         self.surface_size.height = height;