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Fix using mask colour even if there is no mask in wxImage::Paste

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In case an image without alpha is pasted on top of an image with alpha,
the alpha blending gives wrong results. This is caused by the fact that
the final (if nothing has been pasted yet) pixel copying algorithm in
Paste() does not take into account whether the pasted image actually
uses a mask.

To fix this:

- Add the check for image.HasMask().
- In case there is no mask, simply copy the image via memcpy.
- Finally, update the alpha channel of the changed image (if present):
  whenever a pixel is copied, the alpha is set to fully opaque.

Closes https://github.com/wxWidgets/wxWidgets/pull/2065
This commit is contained in:
Eric Raijmakers 2020-09-30 12:09:23 +02:00 committed by Vadim Zeitlin
parent a94fda4503
commit 1f0ade29f0
3 changed files with 127 additions and 24 deletions
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64
src/common/image.cpp
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@ -1739,29 +1739,61 @@ wxImage::Paste(const wxImage & image, int x, int y,
// being pasted into account.
if (!copiedPixels)
{
unsigned char r = image.GetMaskRed();
unsigned char g = image.GetMaskGreen();
unsigned char b = image.GetMaskBlue();
const unsigned char* source_data = image.GetData() + 3 * (xx + yy * image.GetWidth());
int source_step = image.GetWidth() * 3;
const unsigned char* source_data = image.GetData() + 3*(xx + yy*image.GetWidth());
int source_step = image.GetWidth()*3;
unsigned char* target_data = GetData() + 3 * ((x + xx) + (y + yy) * M_IMGDATA->m_width);
int target_step = M_IMGDATA->m_width * 3;
unsigned char* target_data = GetData() + 3*((x+xx) + (y+yy)*M_IMGDATA->m_width);
int target_step = M_IMGDATA->m_width*3;
for (int j = 0; j < height; j++)
unsigned char* alpha_target_data = NULL;
const int target_alpha_step = M_IMGDATA->m_width;
if (HasAlpha())
{
for (int i = 0; i < width*3; i+=3)
alpha_target_data = GetAlpha() + (x + xx) + (y + yy) * M_IMGDATA->m_width;
}
// The mask colours should only be taken into account if the mask is actually enabled
if (!image.HasMask())
{
// Copy all pixels
for (int j = 0; j < height; j++)
{
if ((source_data[i] != r) ||
(source_data[i+1] != g) ||
(source_data[i+2] != b))
memcpy(target_data, source_data, width * 3);
source_data += source_step;
target_data += target_step;
// Make all the copied pixels fully opaque
if (alpha_target_data != NULL)
{
memcpy( target_data+i, source_data+i, 3 );
memset(alpha_target_data, wxALPHA_OPAQUE, target_alpha_step);
alpha_target_data += target_alpha_step;
}
}
source_data += source_step;
target_data += target_step;
}
else
{
// Copy all 'non masked' pixels
unsigned char r = image.GetMaskRed();
unsigned char g = image.GetMaskGreen();
unsigned char b = image.GetMaskBlue();
for (int j = 0; j < height; j++)
{
for (int i = 0; i < width * 3; i += 3)
{
if ((source_data[i] != r) ||
(source_data[i + 1] != g) ||
(source_data[i + 2] != b))
{
// Copy the non masked pixel
memcpy(target_data + i, source_data + i, 3);
// Make the copied pixel fully opaque
alpha_target_data[i / 3] = wxALPHA_OPAQUE;
}
}
source_data += source_step;
target_data += target_step;
alpha_target_data += target_alpha_step;
}
}
}
}

87
tests/image/image.cpp
View File

@ -1460,7 +1460,7 @@ TEST_CASE("wxImage::Paste", "[image][paste]")
{
"9 9 7 1",
" c None",
"y c #FF0000",
"y c #FFFF00",
"r c #FF0000",
"g c #00FF00",
"b c #0000FF",
@ -1481,7 +1481,7 @@ TEST_CASE("wxImage::Paste", "[image][paste]")
{
"9 9 2 1",
" c None",
"y c #FF0000",
"y c #FFFF00",
"y y y y y",
" y y y y ",
"y y y y y",
@ -1508,7 +1508,7 @@ TEST_CASE("wxImage::Paste", "[image][paste]")
{
"13 13 2 1",
" c None",
"y c #FF0000",
"y c #FFFF00",
"y y y y y y y",
" y y y y y y ",
"y y y y y y y",
@ -1537,7 +1537,7 @@ TEST_CASE("wxImage::Paste", "[image][paste]")
{
"5 5 2 1",
" c None",
"y c #FF0000",
"y c #FFFF00",
"y y y",
" y y ",
"y y y",
@ -1549,7 +1549,7 @@ TEST_CASE("wxImage::Paste", "[image][paste]")
{
"9 9 7 1",
" c None",
"y c #FF0000",
"y c #FFFF00",
"r c #FF0000",
"g c #00FF00",
"b c #0000FF",
@ -1579,7 +1579,7 @@ TEST_CASE("wxImage::Paste", "[image][paste]")
{
"9 9 7 1",
" c None",
"y c #FF0000",
"y c #FFFF00",
"r c #FF0000",
"g c #00FF00",
"b c #0000FF",
@ -1609,7 +1609,7 @@ TEST_CASE("wxImage::Paste", "[image][paste]")
{
"9 9 7 1",
" c None",
"y c #FF0000",
"y c #FFFF00",
"r c #FF0000",
"g c #00FF00",
"b c #0000FF",
@ -1667,7 +1667,7 @@ TEST_CASE("wxImage::Paste", "[image][paste]")
{
"9 9 7 1",
" c None",
"y c #FF0000",
"y c #FFFF00",
"r c #FF0000",
"g c #00FF00",
"b c #0000FF",
@ -1768,6 +1768,77 @@ TEST_CASE("wxImage::Paste", "[image][paste]")
CHECK_THAT(actual, RGBSimilarTo(wxImage("image/paste_result_no_background_square_over_circle.png"), 1));
CHECK_THAT(actual, CenterAlphaPixelEquals(224));
}
SECTION("Paste fully transparent (masked) image over light image") // todo make test case for 'blend with mask'
{
const static char* transparent_image_xpm[] =
{
"5 5 2 1",
" c None", // Mask
"y c #FFFF00",
" ",
" ",
" ",
" ",
" ",
};
const static char* light_image_xpm[] =
{
"5 5 2 1",
" c None",
"y c #FFFF00",
"yyyyy",
"yyyyy",
"yyyyy",
"yyyyy",
"yyyyy",
};
wxImage actual(light_image_xpm);
actual.InitAlpha();
wxImage paste(transparent_image_xpm);
wxImage expected(light_image_xpm);
actual.Paste(paste, 0, 0, wxIMAGE_ALPHA_BLEND_COMPOSE);
CHECK_THAT(actual, RGBSameAs(expected));
}
SECTION("Paste fully black (masked) image over light image") // todo make test case for 'blend with mask'
{
const static char* black_image_xpm[] =
{
"5 5 2 1",
" c #000000",
"y c None", // Mask
" ",
" ",
" ",
" ",
" ",
};
const static char* light_image_xpm[] =
{
"5 5 2 1",
" c None",
"y c #FFFF00",
"yyyyy",
"yyyyy",
"yyyyy",
"yyyyy",
"yyyyy",
};
wxImage actual(light_image_xpm);
actual.InitAlpha();
wxImage paste(black_image_xpm);
wxImage expected(black_image_xpm);
actual.Paste(paste, 0, 0, wxIMAGE_ALPHA_BLEND_COMPOSE);
CHECK_THAT(actual, RGBSameAs(expected));
}
SECTION("Paste dark image over light image")
{
wxImage black("image/paste_input_black.png");
wxImage actual("image/paste_input_background.png");
actual.InitAlpha();
actual.Paste(black, 0, 0, wxIMAGE_ALPHA_BLEND_COMPOSE);
CHECK_THAT(actual, CenterAlphaPixelEquals(255));
CHECK_THAT(actual, RGBSameAs(black));
}
}
/*

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