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Frame: Fix interlaced AddImage #418

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Feb 27, 2020
Merged

Frame: Fix interlaced AddImage #418

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23 changes: 15 additions & 8 deletions src/Frame.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -818,16 +818,23 @@ void Frame::AddImage(std::shared_ptr<QImage> new_image, bool only_odd_lines)
// Ignore image of different sizes or formats
bool ret=false;
#pragma omp critical (AddImage)
if (image == new_image || image->size() != image->size() || image->format() != image->format())
ret=true;
if (ret)
{
if (image == new_image || image->size() != new_image->size()) {
ret = true;
}
else if (new_image->format() != image->format()) {
new_image = std::shared_ptr<QImage>(new QImage(new_image->convertToFormat(image->format())));
}
}
if (ret) {
return;

}

// Get the frame's image
const GenericScopedLock<juce::CriticalSection> lock(addingImageSection);
#pragma omp critical (AddImage)
{
const unsigned char *pixels = image->constBits();
unsigned char *pixels = image->bits();
Comment on lines -830 to +837
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consts are nice and all, when appropriate, but when you're modifying the pixels in the buffer I'm pretty sure we're not supposed to use constBits() since it suppresses Qt's copy-on-write handling for shared QImage buffers.

const unsigned char *new_pixels = new_image->constBits();

// Loop through the scanlines of the image (even or odd)
Expand All @@ -836,13 +843,13 @@ void Frame::AddImage(std::shared_ptr<QImage> new_image, bool only_odd_lines)
start = 1;

for (int row = start; row < image->height(); row += 2) {
memcpy((unsigned char *) pixels, new_pixels + (row * image->bytesPerLine()), image->bytesPerLine());
new_pixels += image->bytesPerLine();
int offset = row * image->bytesPerLine();
memcpy(pixels + offset, new_pixels + offset, image->bytesPerLine());
Comment on lines 845 to +847
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This is where things really break.

The way that loop was previously written, it would go through every other row (odd or even) in new_pixels, and copy that row's data to the first row of pixels — every time! Nothing was ever offsetting the pixels location to advance it by the row stride, and nothing would have ever written to any part of pixels (and therefore image) beyond the first scanline/row.

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(Oh, yeah — the telltale cast on pixels — to cast away its const status, which it shouldn't have had in the first place — is also fun, in the previous code.)

}

// Update height and width
width = image->width();
height = image->height();
width = image->width();
has_image_data = true;
}
}
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