Bug 1882890 Part 2 - Add tests for centering the page when printing. r=dholbert

Because the properties of the tests are all just size relations, it's easy
to generate some of the source directly and provide it as a data URL.

This should test all three states for the pref.

Differential Revision: https://phabricator.services.mozilla.com/D204134

layout/base/tests/chrome/chrome.toml

@@ -66,6 +66,12 @@ support-files = [
   "printpreview_pps16_ref.html",
   "printpreview_prettyprint.xml",
   "printpreview_prettyprint_ref.xhtml",
+  "printpreview_scale_test_001.html",
+  "printpreview_scale_test_001_ref.html",
+  "printpreview_scale_test_002.html",
+  "printpreview_scale_test_002_ref.html",
+  "printpreview_scale_test_003.html",
+  "printpreview_scale_test_003_ref.html",
   "printpreview_mask.html",
   "print_page_size1.html",
   "print_page_size1_ref.html",

layout/base/tests/chrome/printpreview_helper.xhtml

@@ -1708,9 +1708,252 @@ async function runTest58() {
   let test = "printpreview_mixed_page_size_002.html";
   // The params are just to give the file unique URLs.
   await compareFiles(test + "?test", test + "?ref");
+  requestAnimationFrame(() => setTimeout(runTest59));
+}
+
+// Creates a data URL that has a single div of |divSize| em square, on a page
+// of size |pageSize| inches square.
+// |center| determines if the div should be centered horizontally.
+function createScalingTestSource(pageSize, center, name) {
+  // Styling always used.
+  let baseStyle = 'background: blue;';
+  if (center) {
+    baseStyle += 'margin: auto;';
+  }
+  const div = '<div style="width: 100px; height: 100px;' + baseStyle + '"></div>';
+  const style = '<style>@page{size:' + pageSize + 'in}body{margin:0}</style>';
+  // Add the name as a comment, to ensure every test has a unique source even
+  // if the parameters are identical.
+  const comment = '<!-- ' + name + ' -->';
+  return 'data:text/html,' + style + div + comment;
+}
+
+async function runScalingCenteredTest(refPageSize, testPageSize, paperSize,
+    name, center = true, fuzz = null) {
+  const printSettings = {
+    settings: {
+      paperWidth: paperSize,
+      paperHeight: paperSize,
+      paperSizeUnit: Ci.nsIPrintSettings.kPaperSizeInches,
+      marginTop: 0,
+      marginRight: 0,
+      marginBottom: 0,
+      marginLeft: 0,
+      unwriteableMarginTop: 0,
+      unwriteableMarginRight: 0,
+      unwriteableMarginBottom: 0,
+      unwriteableMarginLeft: 0,
+    }
+  };
+  let settings = Object.create(fuzz, {
+    ref: {value: printSettings},
+    test: {value: printSettings}
+  });
+  const testSrc = createScalingTestSource(testPageSize, center, name);
+  const refSrc = createScalingTestSource(refPageSize, center, name);
+  return compareFiles(testSrc, refSrc, settings);
+}
+
+// Tests that auto-detection and use of page centering.
+// Has a smaller page on a larger sheet, where the difference is within the
+// tolerance for auto-detection.
+async function runTest59() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["print.center_page_on_sheet", 2]]
+  });
+  // See bug 1680838
+  const fuzz = navigator.platform.includes("Win") ?
+      { maxDifferent: 180, maxDifference: 255 } :
+      null;
+  await runScalingCenteredTest(10, 9.5, 10, "runTest59", true, fuzz);
+  await SpecialPowers.popPrefEnv();
+  requestAnimationFrame(() => setTimeout(runTest60));
+}
+
+// Tests that centering won't occur when the pref disables it, using the same
+// values as runTest59.
+async function runTest60() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["print.center_page_on_sheet", 0]]
+  });
+  // See bug 1680838
+  const fuzz = navigator.platform.includes("Win") ?
+      { maxDifferent: 180, maxDifference: 255 } :
+      null;
+  await runScalingCenteredTest(10, 9.5, 10, "runTest60", false, fuzz);
+  await SpecialPowers.popPrefEnv();
+  requestAnimationFrame(() => setTimeout(runTest61));
+}
+
+// Tests that auto-detection will reject too big a difference for page
+// centering. Has a much smaller page on a larger sheet, where the difference
+// is outside the threshold for auto-detection.
+async function runTest61() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["print.center_page_on_sheet", 2]]
+  });
+  // See bug 1680838
+  const fuzz = navigator.platform.includes("Win") ?
+      { maxDifferent: 450, maxDifference: 255 } :
+      null;
+  await runScalingCenteredTest(10, 8.9, 10, "runTest61", false, fuzz);
+  await SpecialPowers.popPrefEnv();
+  requestAnimationFrame(() => setTimeout(runTest62));
+}
+
+// Tests that we can force page centering with the pref, using the same values
+// as runTest61.
+async function runTest62() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["print.center_page_on_sheet", 1]]
+  });
+  // See bug 1680838
+  const fuzz = navigator.platform.includes("Win") ?
+      { maxDifferent: 450, maxDifference: 255 } :
+      null;
+  await runScalingCenteredTest(10, 8.9, 10, "runTest62", true, fuzz);
+  await SpecialPowers.popPrefEnv();
+  requestAnimationFrame(() => setTimeout(runTest63));
+}
+
+// Tests that centering will always happen if the pref forces it.
+// The sizes used in these files are very large and the scale factor very high
+// here to ensure that any errors in the calculation for centering will be
+// magnified.
+async function runTest63() {
+  let test = "printpreview_scale_test_001.html";
+  let ref = "printpreview_scale_test_001_ref.html";
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["print.center_page_on_sheet", 1]]
+  });
+  await compareFiles(test, ref, {
+    test: {
+      settings: {
+        paperWidth: 8.5,
+        paperHeight: 11,
+        paperSizeUnit: Ci.nsIPrintSettings.kPaperSizeInches,
+        marginTop: 0,
+        marginRight: 0,
+        marginBottom: 0,
+        marginLeft: 0,
+        unwriteableMarginTop: 0,
+        unwriteableMarginRight: 0,
+        unwriteableMarginBottom: 0,
+        unwriteableMarginLeft: 0,
+      },
+    },
+    ref: {
+      settings: {
+        paperWidth: 8.5,
+        paperHeight: 11,
+        paperSizeUnit: Ci.nsIPrintSettings.kPaperSizeInches,
+        marginTop: 0,
+        marginRight: 0,
+        marginBottom: 0,
+        marginLeft: 0,
+        unwriteableMarginTop: 0,
+        unwriteableMarginRight: 0,
+        unwriteableMarginBottom: 0,
+        unwriteableMarginLeft: 0,
+      },
+    },
+  });
+  await SpecialPowers.popPrefEnv();
+  requestAnimationFrame(() => setTimeout(runTest64));
+}
+
+// Tests that printing A4 pages on US Letter will be a close enough fit
+// that we will automatically center the page.
+async function runTest64() {
+  let test = "printpreview_scale_test_002.html";
+  let ref = "printpreview_scale_test_002_ref.html";
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["print.center_page_on_sheet", 2]]
+  });
+  await compareFiles(test, ref, {
+    test: {
+      settings: {
+        paperWidth: 8.5,
+        paperHeight: 11,
+        paperSizeUnit: Ci.nsIPrintSettings.kPaperSizeInches,
+        marginTop: 0,
+        marginRight: 0,
+        marginBottom: 0,
+        marginLeft: 0,
+        unwriteableMarginTop: 0,
+        unwriteableMarginRight: 0,
+        unwriteableMarginBottom: 0,
+        unwriteableMarginLeft: 0,
+      },
+    },
+    ref: {
+      settings: {
+        paperWidth: 8.5,
+        paperHeight: 11,
+        paperSizeUnit: Ci.nsIPrintSettings.kPaperSizeInches,
+        marginTop: 0,
+        marginRight: 0,
+        marginBottom: 0,
+        marginLeft: 0,
+        unwriteableMarginTop: 0,
+        unwriteableMarginRight: 0,
+        unwriteableMarginBottom: 0,
+        unwriteableMarginLeft: 0,
+      },
+    },
+  });
+  await SpecialPowers.popPrefEnv();
+  requestAnimationFrame(() => setTimeout(runTest65));
+}
+
+// Tests that auto-detection will reject a large enough difference in width
+// when downscaling is used to make the page fit on the paper.
+async function runTest65() {
+  let test = "printpreview_scale_test_003.html";
+  let ref = "printpreview_scale_test_003_ref.html";
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["print.center_page_on_sheet", 2]]
+  });
+  await compareFiles(test, ref, {
+    test: {
+      settings: {
+        paperWidth: 8.5,
+        paperHeight: 11,
+        paperSizeUnit: Ci.nsIPrintSettings.kPaperSizeInches,
+        marginTop: 0,
+        marginRight: 0,
+        marginBottom: 0,
+        marginLeft: 0,
+        unwriteableMarginTop: 0,
+        unwriteableMarginRight: 0,
+        unwriteableMarginBottom: 0,
+        unwriteableMarginLeft: 0,
+      },
+    },
+    ref: {
+      settings: {
+        paperWidth: 8.5,
+        paperHeight: 11,
+        paperSizeUnit: Ci.nsIPrintSettings.kPaperSizeInches,
+        marginTop: 0,
+        marginRight: 0,
+        marginBottom: 0,
+        marginLeft: 0,
+        unwriteableMarginTop: 0,
+        unwriteableMarginRight: 0,
+        unwriteableMarginBottom: 0,
+        unwriteableMarginLeft: 0,
+      },
+    },
+  });
+  await SpecialPowers.popPrefEnv();
   finish();
 }
 
+
 ]]></script>
 <table style="border: 1px solid black;" xmlns="http://www.w3.org/1999/xhtml">
 <tr><th>Print preview canvas 1</th><th>Print preview canvas 2</th></tr>

layout/base/tests/chrome/printpreview_scale_test_001.html

@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<head>
+  <style>
+@page {
+  size: 10in 22in;
+  margin: 0;
+}
+body{
+  margin:0;
+}
+div{
+  width: 2in;
+  height: 2in;
+  background: blue;
+  margin-left: 4in;
+}
+  </style>
+</head>
+<body>
+  <div></div>
+</body>

layout/base/tests/chrome/printpreview_scale_test_001_ref.html

@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<head>
+  <style>
+@page {
+  size: 4in 44in;
+  margin: 0;
+}
+body{
+  margin:0;
+}
+div{
+  height: 4in;
+  width: 4in;
+  background: blue;
+}
+  </style>
+</head>
+<body>
+  <div></div>
+</body>

layout/base/tests/chrome/printpreview_scale_test_002.html

@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<head>
+  <style>
+@page {
+  size: A4;
+  margin: 0;
+}
+body{
+  margin:0;
+}
+div{
+  height: 200px;
+  width: 200px;
+  background: blue;
+  margin: auto;
+}
+  </style>
+</head>
+<body>
+  <div></div>
+</body>

layout/base/tests/chrome/printpreview_scale_test_002_ref.html

@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<head>
+  <style>
+@page {
+  size: letter;
+  margin: 0;
+}
+body{
+  margin:0;
+}
+div{
+  /* A4-on-letter requires a 0.9407 downscale. 11in = 279.4mm, and
+   * 279.4mm / 297mm = 0.9407407407..
+   * The unscaled reference case has a 200px square div, so reverse the scale
+   * to match that (rounding to 0.940741)
+   */
+  height: calc(0.940741 * 200px);
+  width: calc(0.940741 * 200px);
+  background: blue;
+  margin: auto;
+}
+  </style>
+</head>
+<body>
+  <div></div>
+</body>

layout/base/tests/chrome/printpreview_scale_test_003.html

@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<head>
+  <style>
+@page {
+  size: 8.5in 13in;
+  margin: 0;
+}
+body{
+  margin:0;
+}
+div{
+  /* 13in / 11in = 1.1818181... */
+  height: calc(1.1818182 * 200px);
+  width: calc(1.1818182 * 200px);
+  background: blue;
+}
+  </style>
+</head>
+<body>
+  <div></div>
+</body>

layout/base/tests/chrome/printpreview_scale_test_003_ref.html

@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<head>
+  <style>
+@page {
+  size: 8.5in 11in;
+  margin: 0;
+}
+body{
+  margin:0;
+}
+div{
+  /* 11in / 13in = 0.8461538 */
+  height: 200px;
+  width: 200px;
+  background: blue;
+}
+  </style>
+</head>
+<body>
+  <div></div>
+</body>