feat: change pgn opacity

src/pages/tools/image/png/change-opacity/service.ts

@@ -1,7 +1,15 @@
-export async function changeOpacity(
-  file: File,
-  opacity: number
-): Promise<File> {
+interface OpacityOptions {
+  opacity: number;
+  mode: 'solid' | 'gradient';
+  gradientType: 'linear' | 'radial';
+  gradientDirection: 'left-to-right' | 'inside-out';
+  areaLeft: number;
+  areaTop: number;
+  areaWidth: number;
+  areaHeight: number;
+}
+
+export async function changeOpacity(file: File, options: OpacityOptions): Promise<File> {
   return new Promise((resolve, reject) => {
     const reader = new FileReader();
     reader.onload = (event) => {
@@ -13,13 +21,14 @@ export async function changeOpacity(
           reject(new Error('Canvas context not supported'));
           return;
         }
-
         canvas.width = img.width;
         canvas.height = img.height;
 
-        ctx.clearRect(0, 0, canvas.width, canvas.height);
-        ctx.globalAlpha = opacity;
-        ctx.drawImage(img, 0, 0);
+        if (options.mode === 'solid') {
+          applySolidOpacity(ctx, img, options);
+        } else {
+          applyGradientOpacity(ctx, img, options);
+        }
 
         canvas.toBlob((blob) => {
           if (blob) {
@@ -31,9 +40,82 @@ export async function changeOpacity(
         }, 'image/png');
       };
       img.onerror = () => reject(new Error('Failed to load image'));
-      img.src = <string>event.target?.result;
+      img.src = event.target?.result as string;
     };
     reader.onerror = () => reject(new Error('Failed to read file'));
     reader.readAsDataURL(file);
   });
 }
+
+function applySolidOpacity(
+  ctx: CanvasRenderingContext2D,
+  img: HTMLImageElement,
+  options: OpacityOptions
+) {
+  ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
+  ctx.globalAlpha = options.opacity;
+  ctx.drawImage(img, 0, 0);
+}
+
+function applyGradientOpacity(
+  ctx: CanvasRenderingContext2D,
+  img: HTMLImageElement,
+  options: OpacityOptions
+) {
+  const { areaLeft, areaTop, areaWidth, areaHeight } = options;
+
+  ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
+  ctx.drawImage(img, 0, 0);
+
+  const gradient = options.gradientType === 'linear'
+    ? createLinearGradient(ctx, options)
+    : createRadialGradient(ctx, options);
+
+  ctx.fillStyle = gradient;
+  ctx.fillRect(areaLeft, areaTop, areaWidth, areaHeight);
+}
+
+function createLinearGradient(
+  ctx: CanvasRenderingContext2D,
+  options: OpacityOptions
+) {
+  const { areaLeft, areaTop, areaWidth, areaHeight } = options;
+  const gradient = ctx.createLinearGradient(
+    areaLeft,
+    areaTop,
+    areaLeft + areaWidth,
+    areaTop
+  );
+  gradient.addColorStop(0, `rgba(255,255,255,${options.opacity})`);
+  gradient.addColorStop(1, 'rgba(255,255,255,0)');
+  return gradient;
+}
+
+function createRadialGradient(
+  ctx: CanvasRenderingContext2D,
+  options: OpacityOptions
+) {
+  const { areaLeft, areaTop, areaWidth, areaHeight } = options;
+  const centerX = areaLeft + areaWidth / 2;
+  const centerY = areaTop + areaHeight / 2;
+  const radius = Math.min(areaWidth, areaHeight) / 2;
+
+  const gradient = ctx.createRadialGradient(
+    centerX,
+    centerY,
+    0,
+    centerX,
+    centerY,
+    radius
+  );
+
+  if (options.gradientDirection === 'inside-out') {
+    gradient.addColorStop(0, `rgba(255,255,255,${options.opacity})`);
+    gradient.addColorStop(1, 'rgba(255,255,255,0)');
+  } else {
+    gradient.addColorStop(0, 'rgba(255,255,255,0)');
+    gradient.addColorStop(1, `rgba(255,255,255,${options.opacity})`);
+  }
+
+  return gradient;
+}