Drop float records the layout has already buried (v6)

src/Mpdf.php

@@ -15375,6 +15375,33 @@ function GetFloatDivInfo($blklvl = 0, $clear = false)
 		return [$l_exists, $r_exists, $l_max, $r_max, $l_width, $r_width];
 	}
 
+	/**
+	 * Record a float that has just been closed, dropping the ones it has buried.
+	 *
+	 * $floatDivs is document-global and was emptied only in the constructor, yet GetFloatDivInfo() reads
+	 * all of it every time a float is placed. A page of floats therefore costs O(n^2) over a long
+	 * document, which is what a report of floated rows looks like.
+	 *
+	 * A float that ended at or above where this one starts can no longer satisfy the
+	 * `$currpos < $f['endpos']` test, since layout only moves forward from here, so it is dropped. The
+	 * comparison is against the incoming start rather than the current cursor because the cursor rewinds
+	 * to the top of the float that has just been written; anything that jumps backwards prunes nothing
+	 * rather than pruning wrongly.
+	 *
+	 * @param array $floatDiv
+	 *
+	 * @return void
+	 */
+	public function addFloatDiv(array $floatDiv)
+	{
+		$this->floatDivs = array_values(array_filter($this->floatDivs, function ($f) use ($floatDiv) {
+			// Only within the same block formatting context: a float elsewhere is still ClearFloats' to find.
+			return $f['blockContext'] !== $floatDiv['blockContext'] || $f['endpos'] > $floatDiv['startpos'];
+		}));
+
+		$this->floatDivs[] = $floatDiv;
+	}
+
 	/* -- END CSS-FLOAT -- */
 
 	// LIST MARKERS	// mPDF 6  Lists

src/Tag/BlockTag.php

@@ -1301,7 +1301,7 @@ public function close(&$ahtml, &$ihtml)
 				}
 			}
 
-			$this->mpdf->floatDivs[] = [
+			$this->mpdf->addFloatDiv([
 				'side' => 'R',
 				'startpage' => $this->mpdf->blk[$this->mpdf->blklvl]['startpage'],
 				'y0' => $this->mpdf->blk[$this->mpdf->blklvl]['float_start_y'],
@@ -1312,7 +1312,7 @@ public function close(&$ahtml, &$ihtml)
 				'w' => $this->mpdf->blk[$this->mpdf->blklvl]['float_width'],
 				'blklvl' => $this->mpdf->blklvl,
 				'blockContext' => $this->mpdf->blk[$this->mpdf->blklvl - 1]['blockContext']
-			];
+			]);
 
 			$this->mpdf->y = $this->mpdf->blk[$this->mpdf->blklvl]['float_start_y'];
 			$this->mpdf->page = $this->mpdf->blk[$this->mpdf->blklvl]['startpage'];
@@ -1336,7 +1336,7 @@ public function close(&$ahtml, &$ihtml)
 				}
 			}
 
-			$this->mpdf->floatDivs[] = [
+			$this->mpdf->addFloatDiv([
 				'side' => 'L',
 				'startpage' => $this->mpdf->blk[$this->mpdf->blklvl]['startpage'],
 				'y0' => $this->mpdf->blk[$this->mpdf->blklvl]['float_start_y'],
@@ -1347,7 +1347,7 @@ public function close(&$ahtml, &$ihtml)
 				'w' => $this->mpdf->blk[$this->mpdf->blklvl]['float_width'],
 				'blklvl' => $this->mpdf->blklvl,
 				'blockContext' => $this->mpdf->blk[$this->mpdf->blklvl - 1]['blockContext']
-			];
+			]);
 
 			$this->mpdf->y = $this->mpdf->blk[$this->mpdf->blklvl]['float_start_y'];
 			$this->mpdf->page = $this->mpdf->blk[$this->mpdf->blklvl]['startpage'];

tests/Mpdf/FloatDivTest.php

@@ -0,0 +1,126 @@
+<?php
+
+namespace Mpdf;
+
+/**
+ * Pruning of $floatDivs, the document-global list of every float the document has closed.
+ *
+ * GetFloatDivInfo() reads all of it every time a float is placed, so the list has to stay bounded or a
+ * long document of floated rows costs O(n^2). What the pruning may not do is move anything on the page,
+ * so most of this compares the rendered pages against Mpdf as it behaved before.
+ */
+class FloatDivTest extends BaseMpdfTest
+{
+
+	/**
+	 * @dataProvider floatLayoutProvider
+	 */
+	public function testTheRenderedPagesAreUnchangedByPruning($html)
+	{
+		$pruned = new Mpdf(['mode' => 'c']);
+		$pruned->WriteHTML($html);
+
+		$unpruned = new UnprunedFloatsMpdf(['mode' => 'c']);
+		$unpruned->WriteHTML($html);
+
+		/* The page content streams, not Output(), which carries a timestamp and a random file ID. */
+		$this->assertSame($unpruned->pages, $pruned->pages);
+		$this->assertSame($unpruned->page, $pruned->page, 'Pruning should not change the page count.');
+
+		$pruned->cleanup();
+		$unpruned->cleanup();
+	}
+
+	public function floatLayoutProvider()
+	{
+		$lorem = 'Body copy long enough to wrap, so each line box has to negotiate with whatever floats are live where it lands. ';
+
+		$rows = static function ($count, $row) {
+			$html = '';
+			for ($i = 0; $i < $count; $i++) {
+				$html .= sprintf($row, $i, $i, $i);
+			}
+
+			return $html;
+		};
+
+		return [
+			// The reported case: a report of floated columns, one cleared row per record.
+			'grid of cleared rows' => [$rows(60, '<div style="clear: both;"><div style="float: left; width: 30%%;">left %d</div><div style="float: left; width: 30%%;">middle %d</div><div style="float: left; width: 30%%;">right %d</div></div>')],
+			'rows cleared by a trailing div' => [$rows(60, '<div style="float: left; width: 45%%;">left %d</div><div style="float: right; width: 45%%;">right %d</div><div style="clear: both;">%d</div>')],
+			'text flowing beside the floats' => [$rows(40, '<div style="float: left; width: 30%%;">left %d</div><div style="float: right; width: 30%%;">right %d</div><p>' . $lorem . '%d</p><div style="clear: both;"></div>')],
+			'clear on one side only' => [$rows(40, '<div style="float: left; width: 30%%;">left %d</div><div style="float: right; width: 30%%;">right %d</div><div style="clear: left;">after %d</div>')],
+			'floats nested inside floats' => [$rows(30, '<div style="clear: both;"><div style="float: left; width: 48%%;"><div style="float: left; width: 45%%;">inner %d</div><div style="float: right; width: 45%%;">inner %d</div><div style="clear: both;"></div></div><div style="float: right; width: 48%%;">outer %d</div></div>')],
+			'floats that are never cleared' => [$rows(60, '<div style="float: left; width: 24%%;">box %d%d%d</div>')],
+			'floats spanning a page break' => [$rows(30, '<div style="clear: both;"><div style="float: left; width: 45%%;">' . str_repeat($lorem, 4) . '%d</div><div style="float: right; width: 45%%;">%d %d</div></div>')],
+			'floats followed by tables' => [$rows(40, '<div style="float: left; width: 30%%;">float %d</div><div style="clear: both;"></div><table><tr><td>cell %d</td><td>' . $lorem . '%d</td></tr></table>')],
+		];
+	}
+
+	public function testTheRenderedPagesAreUnchangedWhenRowsAreWrittenOneCallAtATime()
+	{
+		/* How a report renderer streams: many WriteHTML() calls into one document. */
+		$write = static function (Mpdf $mpdf) {
+			$mpdf->WriteHTML('<div style="clear: both;">head</div>', HTMLParserMode::HTML_BODY, true, false);
+			for ($i = 0; $i < 60; $i++) {
+				$mpdf->WriteHTML(sprintf('<div style="clear: both;"><div style="float: left; width: 45%%;">left %d</div><div style="float: right; width: 45%%;">right %d</div></div>', $i, $i), HTMLParserMode::HTML_BODY, false, false);
+			}
+			$mpdf->WriteHTML('<div style="clear: both;">foot</div>', HTMLParserMode::HTML_BODY, false, true);
+		};
+
+		$pruned = new Mpdf(['mode' => 'c']);
+		$write($pruned);
+
+		$unpruned = new UnprunedFloatsMpdf(['mode' => 'c']);
+		$write($unpruned);
+
+		$this->assertSame($unpruned->pages, $pruned->pages);
+
+		$pruned->cleanup();
+		$unpruned->cleanup();
+	}
+
+	public function testOnlyTheRowBeingLaidOutIsKept()
+	{
+		$html = '';
+		for ($i = 0; $i < 60; $i++) {
+			$html .= sprintf('<div style="clear: both;"><div style="float: left; width: 30%%;">left %d</div><div style="float: left; width: 30%%;">middle %d</div><div style="float: left; width: 30%%;">right %d</div></div>', $i, $i, $i);
+		}
+
+		$this->mpdf->WriteHTML($html);
+
+		/* Three columns, not 60 rows of them. Before pruning this was 180. */
+		$this->assertCount(3, $this->mpdf->floatDivs);
+	}
+
+	public function testAFloatTheTextIsStillFlowingBesideIsKept()
+	{
+		$this->mpdf->WriteHTML('<div style="float: left; width: 40%;">sidebar</div><p>Body copy beside the float.</p>');
+
+		$this->assertCount(1, $this->mpdf->floatDivs);
+	}
+
+	public function testAFloatIsDroppedOnlyOnceTheNextOneStartsBelowIt()
+	{
+		$below = ['side' => 'L', 'startpos' => 1010.0, 'endpos' => 1050.0, 'blockContext' => 2];
+		$this->mpdf->addFloatDiv($below);
+
+		/* Overlaps it, so both are live. */
+		$this->mpdf->addFloatDiv(['side' => 'R', 'startpos' => 1020.0, 'endpos' => 1060.0, 'blockContext' => 2]);
+		$this->assertCount(2, $this->mpdf->floatDivs);
+
+		/* Starts below both, so both are behind the cursor for good. */
+		$this->mpdf->addFloatDiv(['side' => 'L', 'startpos' => 1080.0, 'endpos' => 1090.0, 'blockContext' => 2]);
+		$this->assertCount(1, $this->mpdf->floatDivs);
+	}
+
+	public function testAFloatInAnotherBlockFormattingContextIsKept()
+	{
+		/* ClearFloats() matches on blockContext alone, ignoring position, so another context is not ours to drop. */
+		$this->mpdf->addFloatDiv(['side' => 'L', 'startpos' => 1010.0, 'endpos' => 1050.0, 'blockContext' => 2]);
+		$this->mpdf->addFloatDiv(['side' => 'L', 'startpos' => 1080.0, 'endpos' => 1090.0, 'blockContext' => 3]);
+
+		$this->assertCount(2, $this->mpdf->floatDivs);
+	}
+
+}

tests/Mpdf/UnprunedFloatsMpdf.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace Mpdf;
+
+/**
+ * mPDF as it behaved before dead floats were pruned: every float ever closed is kept and rescanned.
+ *
+ * The baseline FloatDivTest measures the pruning against.
+ */
+class UnprunedFloatsMpdf extends Mpdf
+{
+
+	public function addFloatDiv(array $floatDiv)
+	{
+		$this->floatDivs[] = $floatDiv;
+	}
+
+}