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Text baseline alignment issues #1562

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49e1a79
meh solution
asturur Apr 25, 2020
b2cf3ea
meh solution
asturur Apr 25, 2020
7aeef38
meh solution
asturur Apr 25, 2020
1e3e9c6
new test
asturur Apr 25, 2020
96d5310
remove extra arg
asturur Apr 25, 2020
72a23e1
remove extra arg
asturur Apr 25, 2020
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try
asturur Apr 25, 2020
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changelog
asturur Apr 27, 2020
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Merge branch 'master' into issue-1544-textscaling
asturur Jul 18, 2020
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
* Fix BMP issues. (#1497)
* Update typings to support jpg and addPage on NodeCanvasRenderingContext2D (#1509)
* Fix assertion failure when using Visual Studio Code debugger to inspect Image prototype (#1534)
* Tweak text baseline positioning to be as close as possible to browser canvas (#1562)

2.6.1
==================
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22 changes: 16 additions & 6 deletions src/CanvasRenderingContext2d.cc
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Expand Up @@ -2402,21 +2402,30 @@ NAN_METHOD(Context2d::StrokeText) {
*/
inline double getBaselineAdjustment(PangoLayout* layout, short baseline) {
PangoRectangle logical_rect;
pango_layout_line_get_extents(pango_layout_get_line(layout, 0), NULL, &logical_rect);

PangoLayout* measureLayout = pango_layout_copy(layout);
pango_layout_set_text(measureLayout, "gjĮ測試ÅÊ", -1);
pango_layout_line_get_extents(pango_layout_get_line(measureLayout, 0), NULL, &logical_rect);
double scale = 1.0 / PANGO_SCALE;
double ascent = scale * pango_layout_get_baseline(layout);
double ascent = scale * pango_layout_get_baseline(measureLayout);
double descent = scale * logical_rect.height - ascent;
// 0.072 is a constant that has been chosen comparing the canvas output
// if some code change, this constant can be changed too to keep results aligned
double correction_factor = scale * logical_rect.height * 0.072;

switch (baseline) {
case TEXT_BASELINE_ALPHABETIC:
return ascent;
case TEXT_BASELINE_IDEOGRAPHIC:
return ascent + correction_factor;
case TEXT_BASELINE_MIDDLE:
return (ascent + descent) / 2.0;
case TEXT_BASELINE_BOTTOM:
return ascent + descent;
return (ascent + descent) - correction_factor;
case TEXT_BASELINE_HANGING:
return correction_factor * 3.0;
case TEXT_BASELINE_TOP:
default:
return 0;
return correction_factor;
}
}

Expand All @@ -2443,7 +2452,6 @@ Context2d::setTextPath(double x, double y) {
x -= logical_rect.width;
break;
}

y -= getBaselineAdjustment(_layout, state->textBaseline);

cairo_move_to(_context, x, y);
Expand Down Expand Up @@ -2684,8 +2692,10 @@ NAN_METHOD(Context2d::MeasureText) {
x_offset = 0.0;
}

// are those two line useful?
cairo_matrix_t matrix;
cairo_get_matrix(ctx, &matrix);

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@asturur asturur Apr 27, 2020

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matrix does not seem to be used in the function. Is cairo_get_matrix having some side effect that is necessary for the code below to work?

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@chearon chearon Jul 20, 2020

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It looks like it is used for alphabeticBaseline below

double y_offset = getBaselineAdjustment(layout, context->state->textBaseline);

Nan::Set(obj,
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2 changes: 1 addition & 1 deletion test/canvas.test.js
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Expand Up @@ -947,7 +947,7 @@ describe('Canvas', function () {
assert.ok(metrics.alphabeticBaseline > 0) // ~4-5
assert.ok(metrics.actualBoundingBoxAscent > 0)
// On the baseline or slightly above
assert.ok(metrics.actualBoundingBoxDescent <= 0)
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@asturur asturur Apr 27, 2020

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i tweaked the baseline offset, so i expect some text measurement to change slightly. Unsure if this is ok or not. Any thought anyone?

assert.ok(metrics.actualBoundingBoxDescent <= 1)
});
});

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171 changes: 159 additions & 12 deletions test/public/tests.js
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Expand Up @@ -981,79 +981,217 @@ tests['textAlign center'] = function (ctx) {
tests['textBaseline alphabetic'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.strokeRect(0, 0, 200, 200)
ctx.lineTo(0, 100)
ctx.moveTo(0, 50)
ctx.lineTo(200, 50)
ctx.moveTo(0, 100)
ctx.lineTo(200, 100)
ctx.moveTo(0, 150)
ctx.lineTo(200, 150)
ctx.stroke()

ctx.font = 'normal 20px Arial'
ctx.textBaseline = 'alphabetic'
ctx.textAlign = 'center'
ctx.font = 'normal 30px Arial'
ctx.fillText('alphabetic', 100, 50)
ctx.font = 'normal 30px Verdana'
ctx.fillText('alphabetic', 100, 100)
ctx.font = 'normal 30px "Courier New"'
ctx.fillText('alphabetic', 100, 150)
}

tests['textBaseline top'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.strokeRect(0, 0, 200, 200)
ctx.lineTo(0, 100)
ctx.moveTo(0, 50)
ctx.lineTo(200, 50)
ctx.moveTo(0, 100)
ctx.lineTo(200, 100)
ctx.moveTo(0, 150)
ctx.lineTo(200, 150)
ctx.stroke()

ctx.font = 'normal 20px Arial'
ctx.textBaseline = 'top'
ctx.textAlign = 'center'
ctx.font = 'normal 30px Arial'
ctx.fillText('top', 100, 50)
ctx.font = 'normal 30px Verdana'
ctx.fillText('top', 100, 100)
ctx.font = 'normal 30px "Courier New"'
ctx.fillText('top', 100, 150)
}

tests['textBaseline hanging'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.strokeRect(0, 0, 200, 200)
ctx.lineTo(0, 100)
ctx.moveTo(0, 50)
ctx.lineTo(200, 50)
ctx.moveTo(0, 100)
ctx.lineTo(200, 100)
ctx.moveTo(0, 150)
ctx.lineTo(200, 150)
ctx.stroke()

ctx.font = 'normal 20px Arial'
ctx.textBaseline = 'hanging'
ctx.textAlign = 'center'
ctx.font = 'normal 30px Arial'
ctx.fillText('hanging', 100, 50)
ctx.font = 'normal 30px Verdana'
ctx.fillText('hanging', 100, 100)
ctx.font = 'normal 30px "Courier New"'
ctx.fillText('hanging', 100, 150)
}

tests['textBaseline middle'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.strokeRect(0, 0, 200, 200)
ctx.lineTo(0, 100)
ctx.moveTo(0, 50)
ctx.lineTo(200, 50)
ctx.moveTo(0, 100)
ctx.lineTo(200, 100)
ctx.moveTo(0, 150)
ctx.lineTo(200, 150)
ctx.stroke()

ctx.font = 'normal 20px Arial'
ctx.textBaseline = 'middle'
ctx.textAlign = 'center'
ctx.font = 'normal 30px Arial'
ctx.fillText('middle', 100, 50)
ctx.font = 'normal 30px Verdana'
ctx.fillText('middle', 100, 100)
ctx.font = 'normal 30px "Courier New"'
ctx.fillText('middle', 100, 150)
}

tests['textBaseline ideographic'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.strokeRect(0, 0, 200, 200)
ctx.lineTo(0, 100)
ctx.moveTo(0, 50)
ctx.lineTo(200, 50)
ctx.moveTo(0, 100)
ctx.lineTo(200, 100)
ctx.moveTo(0, 150)
ctx.lineTo(200, 150)
ctx.stroke()

ctx.font = 'normal 20px Arial'
ctx.textBaseline = 'ideographic'
ctx.textAlign = 'center'
ctx.font = 'normal 30px Arial'
ctx.fillText('ideographic', 100, 50)
ctx.font = 'normal 30px Verdana'
ctx.fillText('ideographic', 100, 100)
ctx.font = 'normal 30px "Courier New"'
ctx.fillText('ideographic', 100, 150)
}

tests['textBaseline bottom'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.strokeRect(0, 0, 200, 200)
ctx.lineTo(0, 100)
ctx.moveTo(0, 50)
ctx.lineTo(200, 50)
ctx.moveTo(0, 100)
ctx.lineTo(200, 100)
ctx.moveTo(0, 150)
ctx.lineTo(200, 150)
ctx.stroke()

ctx.font = 'normal 20px Arial'
ctx.textBaseline = 'bottom'
ctx.textAlign = 'center'
ctx.font = 'normal 30px Arial'
ctx.fillText('bottom', 100, 50)
ctx.font = 'normal 30px Verdana'
ctx.fillText('bottom', 100, 100)
ctx.font = 'normal 30px "Courier New"'
ctx.fillText('bottom', 100, 150)
}

tests['textBaseline alphabetic with scale'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.scale(1, 4)
ctx.lineWidth = 0.25
ctx.strokeRect(0, 0, 200, 50)
ctx.lineTo(0, 25)
ctx.lineTo(200, 25)
ctx.stroke()

ctx.font = 'normal 30px Arial'
ctx.textBaseline = 'alphabetic'
ctx.textAlign = 'center'
ctx.fillText('alphabetic', 100, 25)
}

tests['textBaseline top with scale'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.scale(1, 4)
ctx.lineWidth = 0.25
ctx.strokeRect(0, 0, 200, 50)
ctx.lineTo(0, 25)
ctx.lineTo(200, 25)
ctx.stroke()

ctx.font = 'normal 30px Arial'
ctx.textBaseline = 'top'
ctx.textAlign = 'center'
ctx.fillText('top', 100, 25)
}

tests['textBaseline hanging with scale'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.scale(1, 4)
ctx.lineWidth = 0.25
ctx.strokeRect(0, 0, 200, 50)
ctx.lineTo(0, 25)
ctx.lineTo(200, 25)
ctx.stroke()

ctx.font = 'normal 30px Arial'
ctx.textBaseline = 'hanging'
ctx.textAlign = 'center'
ctx.fillText('hanging', 100, 25)
}

tests['textBaseline middle with scale'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.scale(1, 4)
ctx.lineWidth = 0.25
ctx.strokeRect(0, 0, 200, 50)
ctx.lineTo(0, 25)
ctx.lineTo(200, 25)
ctx.stroke()

ctx.font = 'normal 30px Arial'
ctx.textBaseline = 'middle'
ctx.textAlign = 'center'
ctx.fillText('middle', 100, 25)
}

tests['textBaseline ideographic with scale'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.scale(1, 4)
ctx.lineWidth = 0.25
ctx.strokeRect(0, 0, 200, 50)
ctx.lineTo(0, 25)
ctx.lineTo(200, 25)
ctx.stroke()

ctx.font = 'normal 30px Arial'
ctx.textBaseline = 'ideographic'
ctx.textAlign = 'center'
ctx.fillText('ideographic', 100, 25)
}

tests['textBaseline bottom with scale'] = function (ctx) {
ctx.strokeStyle = '#666'
ctx.scale(1, 4)
ctx.lineWidth = 0.25
ctx.strokeRect(0, 0, 200, 50)
ctx.lineTo(0, 25)
ctx.lineTo(200, 25)
ctx.stroke()

ctx.font = 'normal 30px Arial'
ctx.textBaseline = 'bottom'
ctx.textAlign = 'center'
ctx.fillText('bottom', 100, 25)
}

tests['font size px'] = function (ctx) {
Expand Down Expand Up @@ -2506,3 +2644,12 @@ tests['transformed drawimage'] = function (ctx) {
ctx.transform(1.2, 1, 1.8, 1.3, 0, 0)
ctx.drawImage(ctx.canvas, 0, 0)
}

tests['#1544 text scaling issue'] = function (ctx) {
ctx.font = '24px Verdana'
ctx.fillStyle = 'red'
ctx.textAlign = 'left'
ctx.textBaseline = 'top'
ctx.scale(1, 4)
ctx.fillText('2020', 20, 20)
}