gyk · December 24, 2021 03:19 · Dec 24, 2021
diff --git a/load_and_resize_image.rs b/load_and_resize_image.rs
@@ -0,0 +1,87 @@
+  // Improvements over NWG's built-in implementation:
+  //
+  // - High quality interpolation mode
+  // - Crop non-square images
+  fn load_and_resize_image(decoder: &nwg::ImageDecoder, data: &[u8]) -> Result<Bitmap> {
+      use winapi::shared::windef::{HBITMAP, HDC};
+      use winapi::um::wincodec::{
+          IWICBitmapScaler, IWICBitmapSource, WICBitmapInterpolationModeHighQualityCubic,
+      };
+      use winapi::um::wingdi::{
+          BitBlt, CreateCompatibleBitmap, CreateCompatibleDC, DeleteDC, SelectObject, SRCCOPY,
+      };
+
+      let image_frame = decoder.from_stream(data)?.frame(0)?;
+
+      // Resize
+      let (w, h) = image_frame.size();
+      let thumb_size = scaled_thumb_size();
+      let (w, h) = if w >= h {
+          (thumb_size * w / h, thumb_size)
+      } else {
+          (thumb_size, thumb_size * h / w)
+      };
+
+      let bitmap = unsafe {
+          let mut scaler: *mut IWICBitmapScaler = ptr::null_mut();
+          (&*decoder.factory).CreateBitmapScaler(&mut scaler);
+          let image_source = image_frame.frame as *const IWICBitmapSource;
+          (&*scaler).Initialize(
+              image_source,
+              w,
+              h,
+              WICBitmapInterpolationModeHighQualityCubic,
+          );
+          nwg::ImageData {
+              frame: scaler as *mut IWICBitmapSource,
+          }
+          .as_bitmap()?
+      };
+
+      if w == thumb_size && h == thumb_size {
+          return Ok(bitmap);
+      }
+
+      // Crop
+      unsafe {
+          let hdc_null: HDC = mem::zeroed();
+
+          let hdc_src = CreateCompatibleDC(hdc_null);
+          let bmp_src = bitmap.handle;
+          SelectObject(hdc_src, bmp_src);
+
+          let hdc_dst = CreateCompatibleDC(hdc_null);
+          let bmp_dst: HBITMAP =
+              CreateCompatibleBitmap(hdc_src, thumb_size as i32, thumb_size as i32);
+          SelectObject(hdc_dst, bmp_dst as *mut _);
+
+          BitBlt(
+              hdc_dst,
+              0,
+              0,
+              thumb_size as i32,
+              thumb_size as i32,
+              hdc_src,
+              (w - thumb_size) as i32 / 2,
+              (h - thumb_size) as i32 / 2,
+              SRCCOPY,
+          );
+
+          DeleteDC(hdc_src);
+          DeleteDC(hdc_dst);
+
+          #[allow(dead_code)]
+          struct MyBitmap {
+              handle: *mut std::ffi::c_void,
+              owned: bool,
+          }
+
+          let my_bmp = MyBitmap {
+              handle: bmp_dst as *mut _,
+              owned: true,
+          };
+
+          let bmp: Bitmap = mem::transmute(my_bmp);
+          Ok(bmp)
+      }
+  }