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Add support for % in rgb and fix parsing for % in alpha. #2540

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Add support for % in rgb and fix parsing for % in alpha. #2540

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c8ee451
Fix parsing for alpha with percent values. Add support for percent va…
pranav1344 Oct 29, 2025
63090b8
Merge branch 'master' into master
pranav1344 Jan 30, 2026
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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 @@ -16,6 +16,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
* Fix error message HTTP response status code in image src setter
* `roundRect()` shape incorrect when radii were large relative to rectangle size (#2400)
* Reject loadImage when src is null or invalid (#2304)
* Add support for percentage in rgb and rgba parsing. Fix bug with parsing for alpha and percentages.
* Fix compilation on GCC 15 by including <cstdint> (#2545)

3.2.0
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65 changes: 42 additions & 23 deletions src/color.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,6 @@
#include <limits>
#include <map>
#include <string>

// Compatibility with Visual Studio versions prior to VS2015
#if defined(_MSC_VER) && _MSC_VER < 1900
#define snprintf _snprintf
Expand Down Expand Up @@ -153,14 +152,45 @@ wrap_float(T value, T limit) {
// return (value % limit + limit) % limit;
// }

/*
* Parse and clip a percentage value. Returns a float in the range [0, 1].
*/


static bool
check_percentage(const char* str) {
while (*str && *str != '%' && *str != ',' && *str != ' ' && *str != '/') ++str;
return *str == '%';
}

static bool
parse_clipped_percentage(const char** pStr, float *pFraction) {
float percentage;
bool result = parse_css_number(pStr,&percentage);
const char*& str = *pStr;
if (result) {
if (*str == '%') {
++str;
*pFraction = clip(percentage, 0.0f, 100.0f) / 100.0f;
return result;
}
}
return false;
}

/*
* Parse color channel value
*/

static bool
parse_rgb_channel(const char** pStr, uint8_t *pChannel) {
float f_channel;
if (parse_css_number(pStr, &f_channel)) {
bool percentage = check_percentage(*pStr);
if(percentage && parse_clipped_percentage(pStr, &f_channel)) {
int channel = (int) ceil(255 * f_channel);
*pChannel = channel;
return true;
} else if (parse_css_number(pStr, &f_channel)) {
int channel = (int) ceil(f_channel);
*pChannel = clip(channel, 0, 255);
return true;
Expand All @@ -182,24 +212,6 @@ parse_degrees(const char** pStr, float *pDegrees) {
return false;
}

/*
* Parse and clip a percentage value. Returns a float in the range [0, 1].
*/

static bool
parse_clipped_percentage(const char** pStr, float *pFraction) {
float percentage;
bool result = parse_css_number(pStr,&percentage);
const char*& str = *pStr;
if (result) {
if (*str == '%') {
++str;
*pFraction = clip(percentage, 0.0f, 100.0f) / 100.0f;
return result;
}
}
return false;
}

/*
* Macros to help with parsing inside rgba_from_*_string
Expand Down Expand Up @@ -231,13 +243,15 @@ parse_clipped_percentage(const char** pStr, float *pFraction) {
#define ALPHA(NAME) \
if (*str >= '1' && *str <= '9') { \
NAME = 0; \
float n = .1f; \
while(*str >='0' && *str <= '9') { \
NAME += (*str - '0') * n; \
NAME = NAME * 10 + (*str - '0'); \
str++; \
} \
while(*str == ' ')str++; \
if(*str != '%') { \
if(*str == '%') { \
NAME *= 0.01f; \
++str; \
} else { \
NAME = 1; \
} \
} else { \
Expand All @@ -253,6 +267,11 @@ parse_clipped_percentage(const char** pStr, float *pFraction) {
NAME += (*str++ - '0') * n; \
n *= .1f; \
} \
while(*str == ' ')str++; \
if(*str == '%') { \
NAME *= 0.01f; \
++str; \
} \
} \
} \
do {} while (0) // require trailing semicolon
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21 changes: 21 additions & 0 deletions test/canvas.test.js
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Expand Up @@ -232,6 +232,27 @@ describe('Canvas', function () {

ctx.fillStyle = 'rgb( 255, 300.09, 90, 40%)'
assert.equal('rgba(255, 255, 90, 0.40)', ctx.fillStyle)

ctx.fillStyle = 'rgb( 255, 100%, 50%, 60%)'
assert.equal('rgba(255, 255, 128, 0.60)', ctx.fillStyle)

ctx.fillStyle = 'rgb( 255, 20%, 90, 70%)'
assert.equal('rgba(255, 51, 90, 0.70)', ctx.fillStyle)

ctx.fillStyle = 'rgb( 100%, 300%, 90, 50%)'
assert.equal('rgba(255, 255, 90, 0.50)', ctx.fillStyle)

ctx.fillStyle = 'rgb( 100%, 300.09, 90%, 0)'
assert.equal('rgba(255, 255, 230, 0.00)', ctx.fillStyle)

ctx.fillStyle = 'rgb( 100%, 99%, 80% 50%)'
assert.equal('rgba(255, 253, 204, 0.50)', ctx.fillStyle)

ctx.fillStyle = 'rgb( 100%, 99.99%, 40% / 50%)'
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@yisibl yisibl Dec 25, 2025 •
edited
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To my knowledge, this syntax is not supported in CSS or browsers and requires wrapping with calc().

Or use spaces to separate them:

rgb( 100% 99.99% 40% / 50% )

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@pranav1344 pranav1344 Jan 29, 2026

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To my understanding, the slash here is to separate the rgb from alpha. According to CSS specifications the commas are legacy format, but there is no mention of it being unsupported or deprecated.

https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/color_value/rgb

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@yisibl yisibl Jan 30, 2026

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Try~
image

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@pranav1344 pranav1344 Jan 30, 2026

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I checked the MDN for color syntax, and yeah this makes sense. You cannot mix commas and / in the color property, however this was already the case in node-canvas, I just added a test for this.

@zbjornson @chearon is this something that should be fixed by adding formal syntax validation to rgb (and eventually other type) parsing?

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@chearon chearon Jan 30, 2026

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It would be better not to, but it's probably not a big deal to parse the commas with the slash, since users will almost for sure be using one of the two syntaxes. Good to point it out though.

assert.equal('rgba(255, 255, 102, 0.50)', ctx.fillStyle)

ctx.fillStyle = 'rgb( 100%, 33.33%, 66.66%, 2%)'
assert.equal('rgba(255, 85, 170, 0.02)', ctx.fillStyle)
// hsl / hsla tests

ctx.fillStyle = 'hsl(0, 0%, 0%)'
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