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Simplify how the character BBox is scaled in src/display/canvas_dependency_tracker.js

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In many/most PDF documents every glyph will require that the character BBox has scaling/offset applied, which can be made a tiny bit more efficient. In particular:
 - Avoid creating one additional temporary Array for every glyph.
 - Simplify the helper function, since there's no skew-components.
This commit is contained in:
Jonas Jenwald 2026-05-24 12:20:18 +02:00
parent ea18e73de2
commit 59086fa582
1 changed files with 20 additions and 42 deletions
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62
src/display/canvas_dependency_tracker.js
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@ -28,54 +28,32 @@ function expandBBox(array, index, minX, minY, maxX, maxY) {
array[index * 4 + 3] = Math.max(array[index * 4 + 3], maxY);
}
// Apply a scaling matrix to some min/max values.
// If a scaling factor is negative then min and max must be swapped.
function scaleMinMax(transform, minMax) {
function scaleCharBBox(scaleX, scaleY, x, y, bbox) {
let temp;
if (transform[0]) {
if (transform[0] < 0) {
temp = minMax[0];
minMax[0] = minMax[2];
minMax[2] = temp;
if (scaleX) {
if (scaleX < 0) {
temp = bbox[0];
bbox[0] = bbox[2];
bbox[2] = temp;
}
minMax[0] *= transform[0];
minMax[2] *= transform[0];
bbox[0] *= scaleX;
bbox[2] *= scaleX;
if (transform[3] < 0) {
temp = minMax[1];
minMax[1] = minMax[3];
minMax[3] = temp;
if (scaleY < 0) {
temp = bbox[1];
bbox[1] = bbox[3];
bbox[3] = temp;
}
minMax[1] *= transform[3];
minMax[3] *= transform[3];
bbox[1] *= scaleY;
bbox[3] *= scaleY;
} else {
temp = minMax[0];
minMax[0] = minMax[1];
minMax[1] = temp;
temp = minMax[2];
minMax[2] = minMax[3];
minMax[3] = temp;
if (transform[1] < 0) {
temp = minMax[1];
minMax[1] = minMax[3];
minMax[3] = temp;
}
minMax[1] *= transform[1];
minMax[3] *= transform[1];
if (transform[2] < 0) {
temp = minMax[0];
minMax[0] = minMax[2];
minMax[2] = temp;
}
minMax[0] *= transform[2];
minMax[2] *= transform[2];
bbox.fill(0);
}
minMax[0] += transform[4];
minMax[1] += transform[5];
minMax[2] += transform[4];
minMax[3] += transform[5];
bbox[0] += x;
bbox[1] += y;
bbox[2] += x;
bbox[3] += y;
}
// This is computed rathter than hard-coded to keep into
@ -663,7 +641,7 @@ class CanvasDependencyTracker {
computedBBox = [0, 0, 0, 0];
Util.axialAlignedBoundingBox(fontBBox, font.fontMatrix, computedBBox);
if (scale !== 1 || x !== 0 || y !== 0) {
scaleMinMax([scale, 0, 0, -scale, x, y], computedBBox);
scaleCharBBox(scale, -scale, x, y, computedBBox);
}
if (isBBoxTrustworthy) {