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81 lines
2.4 KiB
C++
81 lines
2.4 KiB
C++
// Clip Library
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// Copyright (C) 2020-2024 David Capello
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//
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// This file is released under the terms of the MIT license.
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// Read LICENSE.txt for more information.
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#ifndef CLIP_COMMON_H_INCLUDED
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#define CLIP_COMMON_H_INCLUDED
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#pragma once
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namespace clip {
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namespace details {
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#if CLIP_ENABLE_IMAGE
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inline void divide_rgb_by_alpha(image& img,
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bool hasAlphaGreaterThanZero = false) {
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const image_spec& spec = img.spec();
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bool hasValidPremultipliedAlpha = true;
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for (unsigned long y=0; y<spec.height; ++y) {
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const uint32_t* dst = (uint32_t*)(img.data()+y*spec.bytes_per_row);
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for (unsigned long x=0; x<spec.width; ++x, ++dst) {
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const uint32_t c = *dst;
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const int r = ((c & spec.red_mask ) >> spec.red_shift );
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const int g = ((c & spec.green_mask) >> spec.green_shift);
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const int b = ((c & spec.blue_mask ) >> spec.blue_shift );
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const int a = ((c & spec.alpha_mask) >> spec.alpha_shift);
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if (a > 0)
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hasAlphaGreaterThanZero = true;
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if (r > a || g > a || b > a)
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hasValidPremultipliedAlpha = false;
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}
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}
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for (unsigned long y=0; y<spec.height; ++y) {
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uint32_t* dst = (uint32_t*)(img.data()+y*spec.bytes_per_row);
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for (unsigned long x=0; x<spec.width; ++x, ++dst) {
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const uint32_t c = *dst;
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int r = ((c & spec.red_mask ) >> spec.red_shift );
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int g = ((c & spec.green_mask) >> spec.green_shift);
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int b = ((c & spec.blue_mask ) >> spec.blue_shift );
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int a = ((c & spec.alpha_mask) >> spec.alpha_shift);
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// If all alpha values = 0, we make the image opaque.
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if (!hasAlphaGreaterThanZero) {
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a = 255;
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// We cannot change the image spec (e.g. spec.alpha_mask=0) to
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// make the image opaque, because the "spec" of the image is
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// read-only. The image spec used by the client is the one
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// returned by get_image_spec().
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}
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// If there is alpha information and it's pre-multiplied alpha
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else if (hasValidPremultipliedAlpha) {
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if (a > 0) {
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// Convert it to straight alpha
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r = r * 255 / a;
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g = g * 255 / a;
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b = b * 255 / a;
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}
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}
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*dst =
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(r << spec.red_shift ) |
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(g << spec.green_shift) |
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(b << spec.blue_shift ) |
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(a << spec.alpha_shift);
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}
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}
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}
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#endif // CLIP_ENABLE_IMAGE
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} // namespace details
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} // namespace clip
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#endif // CLIP_H_INCLUDED
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