Avoid extreme sizing / scaling in tiling pattern

The new test file (tiling-pattern-large-steps.pdf) was manually created,
to have the following characteristics:
- Large xstep and ystep (90000)
- Page width is 4000 (which is larger than MAX_PATTERN_SIZE)
- Visually, the page consists of a red rectangle with a black border,
  surrounded by a 50 unit white padding.
- Before patch: blurry; After patch: sharp

Fixes #6496
Fixes #5698
Fixes #1434
Fixes #2825

src/display/pattern_helper.js

@@ -342,8 +342,10 @@ var TilingPattern = (function TilingPatternClosure() {
       // Use width and height values that are as close as possible to the end
       // result when the pattern is used. Too low value makes the pattern look
       // blurry. Too large value makes it look too crispy.
-      var dimx = this.getSizeAndScale(xstep, combinedScale[0]);
+      var dimx = this.getSizeAndScale(xstep, this.ctx.canvas.width,
-      var dimy = this.getSizeAndScale(ystep, combinedScale[1]);
+        combinedScale[0]);
+      var dimy = this.getSizeAndScale(ystep, this.ctx.canvas.height,
+        combinedScale[1]);
 
       var tmpCanvas = owner.cachedCanvases.getCanvas('pattern',
         dimx.size, dimy.size, true);
@@ -368,12 +370,21 @@ var TilingPattern = (function TilingPatternClosure() {
       return tmpCanvas.canvas;
     },
 
-    getSizeAndScale: function TilingPattern_getSizeAndScale(step, scale) {
+    getSizeAndScale:
+        function TilingPattern_getSizeAndScale(step, realOutputSize, scale) {
       // xstep / ystep may be negative -- normalize.
       step = Math.abs(step);
       // MAX_PATTERN_SIZE is used to avoid OOM situation.
-      var size = Math.min(Math.ceil(step * scale), MAX_PATTERN_SIZE);
+      // Use the destination canvas's size if it is bigger than the hard-coded
-      scale = size / step;
+      // limit of MAX_PATTERN_SIZE to avoid clipping patterns that cover the
+      // whole canvas.
+      var maxSize = Math.max(MAX_PATTERN_SIZE, realOutputSize);
+      var size = Math.ceil(step * scale);
+      if (size >= maxSize) {
+        size = maxSize;
+      } else {
+        scale = size / step;
+      }
       return { scale, size, };
     },
 

test/pdfs/.gitignore

@@ -340,3 +340,4 @@
 !issue9972-1.pdf
 !issue9972-2.pdf
 !issue9972-3.pdf
+!tiling-pattern-large-steps.pdf

test/pdfs/tiling-pattern-large-steps.pdf

@@ -0,0 +1,90 @@
+%PDF-1.4
+% A 4000 x 400 PDF with a red square rectangle and 50 units of padding at all sides.
+1 0 obj
+<<
+/Type /Catalog
+/Pages 2 0 R
+>>
+endobj
+2 0 obj
+<<
+/Type /Pages
+/Kids [3 0 R]
+/Count 1
+>>
+endobj
+3 0 obj
+<<
+/Type /Page
+/MediaBox [0.0 0.0 4000 400]
+/Parent 2 0 R
+/Resources 4 0 R
+/Contents 5 0 R
+>>
+endobj
+4 0 obj
+<<
+/Pattern 6 0 R
+/ColorSpace 7 0 R
+>>
+endobj
+5 0 obj
+<<
+/Length 36
+>>
+stream
+50 50 3950 350 re
+/cs1 cs
+/p1 scn
+f
+endstream
+endobj
+6 0 obj
+<<
+/p1 8 0 R
+>>
+endobj
+7 0 obj
+<<
+/cs1 [/Pattern /DeviceRGB]
+>>
+endobj
+8 0 obj
+<<
+/Length 43
+/Type /Pattern
+/PatternType 1
+/Resources <<
+>>
+/BBox [0 0 3950 350]
+/PaintType 1
+/TilingType 1
+/XStep 90000
+/YStep 90000
+>>
+stream
+/DeviceRGB cs
+1 0 0 sc
+50 50 3950 300 re
+B
+endstream
+endobj
+xref
+0 9
+0000000000 65535 f
+0000000094 00000 n
+0000000143 00000 n
+0000000200 00000 n
+0000000309 00000 n
+0000000363 00000 n
+0000000448 00000 n
+0000000479 00000 n
+0000000527 00000 n
+trailer
+<<
+/Root 1 0 R
+/Size 9
+>>
+startxref
+740
+%%EOF

test/test_manifest.json

@@ -2996,6 +2996,14 @@
        "link": false,
        "type": "eq"
     },
+    {
+       "id": "tiling-pattern-large-steps",
+       "file": "pdfs/tiling-pattern-large-steps.pdf",
+       "md5": "569aac1303c97004aab6a720d9b259b4",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "issue6151",
        "file": "pdfs/issue6151.pdf",
        "md5": "926f8c6b25e6f0978759f7947d70e079",