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Weight pixels by their respective alpha value in wxImage::ResampleBox

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Without this weighting, even the color value of invisible pixels with a zero
alpha would influence the result.

Closes #17724.
This commit is contained in:
Tim Kosse 2016-11-21 17:35:53 +01:00 committed by Vadim Zeitlin
parent 7684f92083
commit b99ad85b6f
2 changed files with 35 additions and 9 deletions
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1
docs/changes.txt
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@ -114,6 +114,7 @@ All (GUI):
- Fix calculating point position in wxDataViewCtrl::HitTest().
- Fix position of the rectangle returned by wxDataViewCtrl::GetItemRect().
- Add wxDataViewRenderer::GetAccessibleDescription().
- Improve wxImage::Scale() handling of pixels with alpha channel (Tim Kosse).
wxGTK:

43
src/common/image.cpp
View File

@ -659,23 +659,48 @@ wxImage wxImage::ResampleBox(int width, int height) const
// Calculate the actual index in our source pixels
src_pixel_index = j * M_IMGDATA->m_width + i;
sum_r += src_data[src_pixel_index * 3 + 0];
sum_g += src_data[src_pixel_index * 3 + 1];
sum_b += src_data[src_pixel_index * 3 + 2];
if ( src_alpha )
if (src_alpha)
{
sum_r += src_data[src_pixel_index * 3 + 0] * src_alpha[src_pixel_index];
sum_g += src_data[src_pixel_index * 3 + 1] * src_alpha[src_pixel_index];
sum_b += src_data[src_pixel_index * 3 + 2] * src_alpha[src_pixel_index];
sum_a += src_alpha[src_pixel_index];
}
else
{
sum_r += src_data[src_pixel_index * 3 + 0];
sum_g += src_data[src_pixel_index * 3 + 1];
sum_b += src_data[src_pixel_index * 3 + 2];
}
averaged_pixels++;
}
}
// Calculate the average from the sum and number of averaged pixels
dst_data[0] = (unsigned char)(sum_r / averaged_pixels);
dst_data[1] = (unsigned char)(sum_g / averaged_pixels);
dst_data[2] = (unsigned char)(sum_b / averaged_pixels);
dst_data += 3;
if ( src_alpha )
if (src_alpha)
{
if (sum_a)
{
dst_data[0] = (unsigned char)(sum_r / sum_a);
dst_data[1] = (unsigned char)(sum_g / sum_a);
dst_data[2] = (unsigned char)(sum_b / sum_a);
}
else
{
dst_data[0] = 0;
dst_data[1] = 0;
dst_data[2] = 0;
}
*dst_alpha++ = (unsigned char)(sum_a / averaged_pixels);
}
else
{
dst_data[0] = (unsigned char)(sum_r / averaged_pixels);
dst_data[1] = (unsigned char)(sum_g / averaged_pixels);
dst_data[2] = (unsigned char)(sum_b / averaged_pixels);
}
dst_data += 3;
}
}