feat(pos): add canvas-based logo rasterization for ePOS-Print

public/pos/epos-print.js

@@ -24,5 +24,49 @@ window.EposPrint = (function () {
     localStorage.setItem(SETTINGS_KEY, JSON.stringify(settings));
   }
 
-  return { getSettings, setSettings };
+  // Rasterize a same-origin image into the packed 1bpp bitmap the
+  // ePOS-Print <image> tag expects. targetWidth must be a multiple of
+  // 8; 384 is the width verified against the shop's TM-T20II.
+  function imageToRaster(url, targetWidth) {
+    return new Promise((resolve, reject) => {
+      const img = new Image();
+      img.onload = () => {
+        const targetHeight = Math.round(img.height * targetWidth / img.width);
+        const canvas = document.createElement('canvas');
+        canvas.width = targetWidth;
+        canvas.height = targetHeight;
+        const ctx = canvas.getContext('2d');
+        ctx.fillStyle = '#fff';
+        ctx.fillRect(0, 0, targetWidth, targetHeight);
+        ctx.drawImage(img, 0, 0, targetWidth, targetHeight);
+        let imageData;
+        try {
+          imageData = ctx.getImageData(0, 0, targetWidth, targetHeight);
+        } catch (e) {
+          reject(new Error('Could not read logo pixels (cross-origin image?): ' + e.message));
+          return;
+        }
+        const data = imageData.data;
+        const rowBytes = Math.ceil(targetWidth / 8);
+        const packed = new Uint8Array(rowBytes * targetHeight);
+        for (let y = 0; y < targetHeight; y++) {
+          for (let x = 0; x < targetWidth; x++) {
+            const i = (y * targetWidth + x) * 4;
+            const luminance = data[i] * 0.3 + data[i + 1] * 0.59 + data[i + 2] * 0.11;
+            const alpha = data[i + 3];
+            if (alpha > 128 && luminance < 128) {
+              packed[y * rowBytes + (x >> 3)] |= 0x80 >> (x % 8);
+            }
+          }
+        }
+        let binary = '';
+        for (let i = 0; i < packed.length; i++) binary += String.fromCharCode(packed[i]);
+        resolve({ width: targetWidth, height: targetHeight, base64: btoa(binary) });
+      };
+      img.onerror = () => reject(new Error('Could not load logo image: ' + url));
+      img.src = url;
+    });
+  }
+
+  return { getSettings, setSettings, imageToRaster };
 })();