[librsvg/librsvg-2.40] bgo#603550 - Compute the luminance correctly when generating a mask
- From: Federico Mena Quintero <federico src gnome org>
- To: commits-list gnome org
- Cc:
- Subject: [librsvg/librsvg-2.40] bgo#603550 - Compute the luminance correctly when generating a mask
- Date: Wed, 4 Oct 2017 15:16:43 +0000 (UTC)
commit 84f7a64179615a23936022cde148e109ecd56b50
Author: Federico Mena Quintero <federico gnome org>
Date: Mon Dec 12 15:19:42 2016 -0600
bgo#603550 - Compute the luminance correctly when generating a mask
Thanks to Mike Lewis for the patch.
https://bugzilla.gnome.org/show_bug.cgi?id=603550
rsvg-cairo-draw.c | 25 ++++-
.../reftests/bugs/603550-mask-luminance-ref.png | Bin 0 -> 4502 bytes
.../reftests/bugs/603550-mask-luminance.svg | 130 ++++++++++++++++++++
3 files changed, 152 insertions(+), 3 deletions(-)
---
diff --git a/rsvg-cairo-draw.c b/rsvg-cairo-draw.c
index 6c6df1c..c29d071 100644
--- a/rsvg-cairo-draw.c
+++ b/rsvg-cairo-draw.c
@@ -770,9 +770,28 @@ rsvg_cairo_generate_mask (cairo_t * cr, RsvgMask * self, RsvgDrawingCtx * ctx, R
guint8 *row_data = (pixels + (row * rowstride));
for (i = 0; i < width; i++) {
guint32 *pixel = (guint32 *) row_data + i;
- *pixel = ((((*pixel & 0x00ff0000) >> 16) * 13817 +
- ((*pixel & 0x0000ff00) >> 8) * 46518 +
- ((*pixel & 0x000000ff)) * 4688) * state->opacity);
+ /*
+ * Assuming, the pixel is linear RGB (not sRGB)
+ * y = luminance
+ * Y = 0.2126 R + 0.7152 G + 0.0722 B
+ * 1.0 opacity = 255
+ *
+ * When Y = 1.0, pixel for mask should be 0xFFFFFFFF
+ * (you get 1.0 luminance from 255 from R, G and B)
+ *
+ * r_mult = 0xFFFFFFFF / (255.0 * 255.0) * .2126 = 14042.45 ~= 14042
+ * g_mult = 0xFFFFFFFF / (255.0 * 255.0) * .7152 = 47239.69 ~= 47240
+ * b_mult = 0xFFFFFFFF / (255.0 * 255.0) * .0722 = 4768.88 ~= 4769
+ *
+ * This allows for the following expected behaviour:
+ * (we only care about the most sig byte)
+ * if pixel = 0x00FFFFFF, pixel' = 0xFF......
+ * if pixel = 0x00020202, pixel' = 0x02......
+ * if pixel = 0x00000000, pixel' = 0x00......
+ */
+ *pixel = ((((*pixel & 0x00ff0000) >> 16) * 14042 +
+ ((*pixel & 0x0000ff00) >> 8) * 47240 +
+ ((*pixel & 0x000000ff) ) * 4769 ) * state->opacity);
}
}
diff --git a/tests/fixtures/reftests/bugs/603550-mask-luminance-ref.png
b/tests/fixtures/reftests/bugs/603550-mask-luminance-ref.png
new file mode 100644
index 0000000..0f16941
Binary files /dev/null and b/tests/fixtures/reftests/bugs/603550-mask-luminance-ref.png differ
diff --git a/tests/fixtures/reftests/bugs/603550-mask-luminance.svg
b/tests/fixtures/reftests/bugs/603550-mask-luminance.svg
new file mode 100644
index 0000000..19c40b2
--- /dev/null
+++ b/tests/fixtures/reftests/bugs/603550-mask-luminance.svg
@@ -0,0 +1,130 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+ xmlns:svg="http://www.w3.org/2000/svg";
+ xmlns="http://www.w3.org/2000/svg";
+ width="744.09448819"
+ height="1052.3622047">
+ <defs
+ id="defs34">
+ <mask
+ maskUnits="userSpaceOnUse"
+ id="masky"
+ x="0"
+ y="0"
+ width='500'
+ height='500'>
+ <g>
+ <rect
+ style="fill:white; stroke:none"
+ id="rect128"
+ width="500"
+ height="500"
+ x="0"
+ y="0" />
+ </g>
+ </mask>
+ </defs>
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <rect
+ style="fill:#000000;fill-opacity:1;stroke:none"
+ id="rect42"
+ width="600"
+ height="300"
+ x="0"
+ y="0"/>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <g mask="url(#masky)" >
+ <rect
+ style="fill:#000000;fill-opacity:1;stroke:none"
+ id="rect42"
+ width="600"
+ height="300"
+ x="0"
+ y="300"/>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ </g>
+ <rect
+ style="fill:#000000;fill-opacity:1;stroke:none"
+ id="rect42"
+ width="50"
+ height="600"
+ x="275"
+ y="0"/>
+</svg>
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