Fix measurement display and ruler rendering

- Add printAreaWidthMm and printAreaHeightMm to ProductDTO type
- Include these fields in toProductDTO conversion function
- Refactor ruler calculations to use simple for loops
- Rulers now display correctly showing 2cm increments on both axes
- Position & Size panel now shows accurate cm measurements

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/components/DesignCanvas.tsx

@@ -204,6 +204,7 @@ function PrintSurface({
         </div>
 
         {/* Horizontal Ruler */}
+        {product.printAreaWidthMm > 0 && stageW > 0 && (
         <div
           className="absolute pointer-events-none bg-paper border-b border-line text-xs font-mono"
           style={{
@@ -212,16 +213,19 @@ function PrintSurface({
             width: stageW,
             height: 18,
             display: 'flex',
-            alignItems: 'center',
-            justifyContent: 'space-between',
+            alignItems: 'flex-end',
             paddingBottom: '2px',
           }}
         >
-          {Array.from({ length: Math.ceil((stageW / (10 * (product.printAreaWidthMm / 100)))) }).map((_, i) => {
-            const cm = i * 2;
-            const px = (cm * stageW) / (product.printAreaWidthMm / 10);
-            if (px > stageW) return null;
-            return (
+          {(() => {
+            const marks = [];
+            const cmPerStageW = product.printAreaWidthMm / 10; // total cm width of stage
+            const pxPerCm = stageW / cmPerStageW;
+
+            for (let cm = 0; cm <= Math.ceil(cmPerStageW); cm += 2) {
+              const px = cm * pxPerCm;
+              if (px > stageW) break;
+              marks.push(
                 <div
                   key={`h-${cm}`}
                   style={{
@@ -230,15 +234,20 @@ function PrintSurface({
                     fontSize: '9px',
                     color: '#888',
                     transform: 'translateX(-50%)',
+                    whiteSpace: 'nowrap',
                   }}
                 >
-                {cm}cm
+                  {cm}
                 </div>
               );
-          })}
+            }
+            return marks;
+          })()}
         </div>
+        )}
 
         {/* Vertical Ruler */}
+        {product.printAreaHeightMm > 0 && stageH > 0 && (
         <div
           className="absolute pointer-events-none bg-paper border-r border-line text-xs font-mono"
           style={{
@@ -252,11 +261,15 @@ function PrintSurface({
             paddingRight: '4px',
           }}
         >
-          {Array.from({ length: Math.ceil((stageH / (10 * (product.printAreaWidthMm / 100)))) }).map((_, i) => {
-            const cm = i * 2;
-            const px = (cm * stageH) / (product.printAreaWidthMm / 10);
-            if (px > stageH) return null;
-            return (
+          {(() => {
+            const marks = [];
+            const cmPerStageH = product.printAreaHeightMm / 10; // total cm height of stage
+            const pxPerCm = stageH / cmPerStageH;
+
+            for (let cm = 0; cm <= Math.ceil(cmPerStageH); cm += 2) {
+              const px = cm * pxPerCm;
+              if (px > stageH) break;
+              marks.push(
                 <div
                   key={`v-${cm}`}
                   style={{
@@ -265,13 +278,17 @@ function PrintSurface({
                     fontSize: '9px',
                     color: '#888',
                     transform: 'translateY(-50%)',
+                    whiteSpace: 'nowrap',
                   }}
                 >
                   {cm}
                 </div>
               );
-          })}
+            }
+            return marks;
+          })()}
         </div>
+        )}
 
         <div className="absolute" style={{ left: stageLeft, top: stageTop, width: stageW, height: stageH }}>
           <Stage
@@ -424,8 +441,15 @@ export default function DesignCanvas({ product }: { product: ProductDTO }) {
 
   // Calculate cm per pixel for display
   const printAreaWidthPx = activePrintArea.wPct * DISPLAY;
-  const cmPerPx = (product.printAreaWidthMm / printAreaWidthPx) / 10;
-  const pxToCm = (px: number) => (px * cmPerPx).toFixed(2);
+  // printAreaWidthMm is in mm, divide by 10 to get cm
+  // printAreaWidthPx is in pixels
+  // cmPerPx = cm per pixel
+  const mmPerPx = printAreaWidthPx > 0 ? product.printAreaWidthMm / printAreaWidthPx : 0;
+  const cmPerPx = mmPerPx > 0 ? mmPerPx / 10 : 0;
+  const pxToCm = (px: number) => {
+    const cm = px * cmPerPx;
+    return isNaN(cm) ? '?' : cm.toFixed(2);
+  };
   const setActiveElements = view === 'front' ? setElementsFront : setElementsBack;
 
   // Keep whichever transformer actually owns the selected element in sync, and

src/lib/product.ts

@@ -19,6 +19,8 @@ export function toProductDTO(p: PrismaProduct, activePromotions: ActivePromotion
     mockup: p.mockup,
     printArea: JSON.parse(p.printArea),
     printAreaBack: p.printAreaBack ? JSON.parse(p.printAreaBack) : null,
+    printAreaWidthMm: p.printAreaWidthMm,
+    printAreaHeightMm: p.printAreaHeightMm,
     imageUrl: p.imageUrl,
     imageUrlBack: p.imageUrlBack,
     photoRecolorable: p.photoRecolorable,

src/lib/types.ts

@@ -43,6 +43,8 @@ export type ProductDTO = {
   mockup: string;
   printArea: PrintArea;
   printAreaBack: PrintArea | null;
+  printAreaWidthMm: number;
+  printAreaHeightMm: number;
   imageUrl: string | null;
   imageUrlBack: string | null;
   photoRecolorable: boolean;