tests/gtest/avifincrtest_helpers.cc - libavif - Git at Google

 // Copyright 2022 Google LLC. All rights reserved.
 // SPDX-License-Identifier: BSD-2-Clause

 #include "avif/avif.h"

 #include <algorithm>
 #include <vector>

 #include "avifincrtest_helpers.h"
 #include "aviftest_helpers.h"
 #include "gtest/gtest.h"

 namespace libavif
 {
 namespace testutil
 {
 namespace
 {

 //------------------------------------------------------------------------------

 // Verifies that the first (top) rowCount rows of image1 and image2 are identical.
 void comparePartialYUVA(const avifImage & image1, const avifImage & image2, uint32_t rowCount)
 {
     if (rowCount == 0) {
         return;
     }
     ASSERT_EQ(image1.width, image2.width);
     ASSERT_GE(image1.height, rowCount);
     ASSERT_GE(image2.height, rowCount);
     ASSERT_EQ(image1.depth, image2.depth);
     ASSERT_EQ(image1.yuvFormat, image2.yuvFormat);
     ASSERT_EQ(image1.yuvRange, image2.yuvRange);

     avifPixelFormatInfo info;
     avifGetPixelFormatInfo(image1.yuvFormat, &info);
     const uint32_t uvWidth = (image1.width + info.chromaShiftX) >> info.chromaShiftX;
     const uint32_t uvHeight = (rowCount + info.chromaShiftY) >> info.chromaShiftY;
     const uint32_t pixelByteCount = (image1.depth > 8) ? sizeof(uint16_t) : sizeof(uint8_t);

     for (uint32_t plane = 0; plane < (info.monochrome ? 1 : AVIF_PLANE_COUNT_YUV); ++plane) {
         const uint32_t width = (plane == AVIF_CHAN_Y) ? image1.width : uvWidth;
         const uint32_t widthByteCount = width * pixelByteCount;
         const uint32_t height = (plane == AVIF_CHAN_Y) ? rowCount : uvHeight;
         const uint8_t * data1 = image1.yuvPlanes[plane];
         const uint8_t * data2 = image2.yuvPlanes[plane];
         for (uint32_t y = 0; y < height; ++y) {
             ASSERT_TRUE(std::equal(data1, data1 + widthByteCount, data2));
             data1 += image1.yuvRowBytes[plane];
             data2 += image2.yuvRowBytes[plane];
         }
     }

     if (image1.alphaPlane) {
         ASSERT_NE(image2.alphaPlane, nullptr);
         ASSERT_EQ(image1.alphaPremultiplied, image2.alphaPremultiplied);
         const uint32_t widthByteCount = image1.width * pixelByteCount;
         const uint8_t * data1 = image1.alphaPlane;
         const uint8_t * data2 = image2.alphaPlane;
         for (uint32_t y = 0; y < rowCount; ++y) {
             ASSERT_TRUE(std::equal(data1, data1 + widthByteCount, data2));
             data1 += image1.alphaRowBytes;
             data2 += image2.alphaRowBytes;
         }
     }
 }

 // Returns the expected number of decoded rows when availableByteCount out of byteCount were
 // given to the decoder, for an image of height rows, split into cells of cellHeight rows.
 uint32_t getMinDecodedRowCount(uint32_t height, uint32_t cellHeight, bool hasAlpha, size_t availableByteCount, size_t byteCount)
 {
     // The whole image should be available when the full input is.
     if (availableByteCount >= byteCount) {
         return height;
     }
     // All but one cell should be decoded if at most 10 bytes are missing.
     if ((availableByteCount + 10) >= byteCount) {
         return height - cellHeight;
     }

     // Subtract the header because decoding it does not output any pixel.
     // Most AVIF headers are below 500 bytes.
     if (availableByteCount <= 500) {
         return 0;
     }
     availableByteCount -= 500;
     byteCount -= 500;
     // Alpha, if any, is assumed to be located before the other planes and to
     // represent at most 50% of the payload.
     if (hasAlpha) {
         if (availableByteCount <= (byteCount / 2)) {
             return 0;
         }
         availableByteCount -= byteCount / 2;
         byteCount -= byteCount / 2;
     }
     // Linearly map the input availability ratio to the decoded row ratio.
     const uint32_t minDecodedCellRowCount = (height / cellHeight) * availableByteCount / byteCount;
     const uint32_t minDecodedPxRowCount = minDecodedCellRowCount * cellHeight;
     // One cell is the incremental decoding granularity.
     // It is unlikely that bytes are evenly distributed among cells. Offset two of them.
     if (minDecodedPxRowCount <= (2 * cellHeight)) {
         return 0;
     }
     return minDecodedPxRowCount - 2 * cellHeight;
 }

 //------------------------------------------------------------------------------

 struct avifROPartialData
 {
     avifROData available;
     size_t fullSize;
 };

 // Implementation of avifIOReadFunc simulating a stream from an array. See avifIOReadFunc documentation.
 // io->data is expected to point to avifROPartialData.
 avifResult avifIOPartialRead(struct avifIO * io, uint32_t readFlags, uint64_t offset, size_t size, avifROData * out)
 {
     const avifROPartialData * data = (avifROPartialData *)io->data;
     if ((readFlags != 0) || !data || (data->fullSize < offset)) {
         return AVIF_RESULT_IO_ERROR;
     }
     if (data->fullSize < (offset + size)) {
         size = data->fullSize - offset;
     }
     if (data->available.size < (offset + size)) {
         return AVIF_RESULT_WAITING_ON_IO;
     }
     out->data = data->available.data + offset;
     out->size = size;
     return AVIF_RESULT_OK;
 }

 //------------------------------------------------------------------------------

 // Encodes the image as a grid of at most gridCols*gridRows cells.
 // The cell count is reduced to fit libavif or AVIF format constraints. If impossible, the encoded output is returned empty.
 // The final cellWidth and cellHeight are output.
 void encodeAsGrid(const avifImage & image, uint32_t gridCols, uint32_t gridRows, avifRWData * output, uint32_t * cellWidth, uint32_t * cellHeight)
 {
     // Chroma subsampling requires even dimensions. See ISO 23000-22 - 7.3.11.4.2
     const bool needEvenWidths = ((image.yuvFormat == AVIF_PIXEL_FORMAT_YUV420) || (image.yuvFormat == AVIF_PIXEL_FORMAT_YUV422));
     const bool needEvenHeights = (image.yuvFormat == AVIF_PIXEL_FORMAT_YUV420);

     ASSERT_GT(gridCols * gridRows, 0u);
     *cellWidth = image.width / gridCols;
     *cellHeight = image.height / gridRows;

     // avifEncoderAddImageGrid() only accepts grids that evenly split the image into cells at least 64 pixels wide and tall.
     while ((gridCols > 1) &&
            (((*cellWidth * gridCols) != image.width) || (*cellWidth < 64) || (needEvenWidths && ((*cellWidth & 1) != 0)))) {
         --gridCols;
         *cellWidth = image.width / gridCols;
     }
     while ((gridRows > 1) &&
            (((*cellHeight * gridRows) != image.height) || (*cellHeight < 64) || (needEvenHeights && ((*cellHeight & 1) != 0)))) {
         --gridRows;
         *cellHeight = image.height / gridRows;
     }

     std::vector<testutil::avifImagePtr> cellImages;
     cellImages.reserve(gridCols * gridRows);
     for (uint32_t row = 0, iCell = 0; row < gridRows; ++row) {
         for (uint32_t col = 0; col < gridCols; ++col, ++iCell) {
             avifCropRect cell;
             cell.x = col * *cellWidth;
             cell.y = row * *cellHeight;
             cell.width = ((cell.x + *cellWidth) <= image.width) ? *cellWidth : (image.width - cell.x);
             cell.height = ((cell.y + *cellHeight) <= image.height) ? *cellHeight : (image.height - cell.y);
             cellImages.emplace_back(avifImageCreateEmpty(), avifImageDestroy);
             ASSERT_NE(cellImages.back(), nullptr);
             ASSERT_EQ(avifImageSetViewRect(cellImages.back().get(), &image, &cell), AVIF_RESULT_OK);
         }
     }

     testutil::avifEncoderPtr encoder(avifEncoderCreate(), avifEncoderDestroy);
     ASSERT_NE(encoder, nullptr);
     encoder->speed = AVIF_SPEED_FASTEST;
     std::vector<avifImage *> cellImagePtrs(cellImages.size()); // Just here to match libavif API.
     for (size_t i = 0; i < cellImages.size(); ++i) {
         cellImagePtrs[i] = cellImages[i].get();
     }
     ASSERT_EQ(avifEncoderAddImageGrid(encoder.get(), gridCols, gridRows, cellImagePtrs.data(), AVIF_ADD_IMAGE_FLAG_SINGLE), AVIF_RESULT_OK);
     ASSERT_EQ(avifEncoderFinish(encoder.get(), output), AVIF_RESULT_OK);
 }

 // Encodes the image to be decoded incrementally.
 void encodeAsIncremental(const avifImage & image, bool flatCells, avifRWData * output, uint32_t * cellWidth, uint32_t * cellHeight)
 {
     const uint32_t gridCols = image.width / 64; // 64px is the min cell width.
     const uint32_t gridRows = flatCells ? 1 : (image.height / 64);
     encodeAsGrid(image, (gridCols > 1) ? gridCols : 1, (gridRows > 1) ? gridRows : 1, output, cellWidth, cellHeight);
 }

 } // namespace

 void encodeRectAsIncremental(const avifImage & image,
                              uint32_t width,
                              uint32_t height,
                              bool createAlphaIfNone,
                              bool flatCells,
                              avifRWData * output,
                              uint32_t * cellWidth,
                              uint32_t * cellHeight)
 {
     avifImagePtr subImage(avifImageCreateEmpty(), avifImageDestroy);
     ASSERT_NE(subImage, nullptr);
     ASSERT_LE(width, image.width);
     ASSERT_LE(height, image.height);
     avifPixelFormatInfo info;
     avifGetPixelFormatInfo(image.yuvFormat, &info);
     const avifCropRect rect {
         /*x=*/((image.width - width) / 2) & ~info.chromaShiftX, /*y=*/((image.height - height) / 2) & ~info.chromaShiftX, width, height
     };
     ASSERT_EQ(avifImageSetViewRect(subImage.get(), &image, &rect), AVIF_RESULT_OK);
     if (createAlphaIfNone && !subImage->alphaPlane) {
         ASSERT_NE(image.yuvPlanes[AVIF_CHAN_Y], nullptr) << "No luma plane to simulate an alpha plane";
         subImage->alphaPlane = image.yuvPlanes[AVIF_CHAN_Y];
         subImage->alphaRowBytes = image.yuvRowBytes[AVIF_CHAN_Y];
         subImage->alphaPremultiplied = AVIF_FALSE;
         subImage->imageOwnsAlphaPlane = AVIF_FALSE;
     }
     encodeAsIncremental(*subImage, flatCells, output, cellWidth, cellHeight);
 }

 //------------------------------------------------------------------------------

 void decodeIncrementally(const avifRWData & encodedAvif,
                          bool isPersistent,
                          bool giveSizeHint,
                          bool useNthImageApi,
                          const avifImage & reference,
                          uint32_t cellHeight)
 {
     // AVIF cells are at least 64 pixels tall.
     if (cellHeight != reference.height) {
         ASSERT_GE(cellHeight, 64u);
     }

     // Emulate a byte-by-byte stream.
     avifROPartialData data = { /*available=*/ { encodedAvif.data, 0 }, /*fullSize=*/encodedAvif.size };
     avifIO io = { /*destroy=*/nullptr, avifIOPartialRead,
                   /*write=*/nullptr,   giveSizeHint ? encodedAvif.size : 0,
                   isPersistent,        &data };

     testutil::avifDecoderPtr decoder(avifDecoderCreate(), avifDecoderDestroy);
     ASSERT_NE(decoder, nullptr);
     avifDecoderSetIO(decoder.get(), &io);
     decoder->allowIncremental = AVIF_TRUE;

     // Parsing is not incremental.
     avifResult parseResult = avifDecoderParse(decoder.get());
     while (parseResult == AVIF_RESULT_WAITING_ON_IO) {
         ASSERT_LT(data.available.size, data.fullSize) << "avifDecoderParse() returned WAITING_ON_IO instead of OK";
         data.available.size = data.available.size + 1;
         parseResult = avifDecoderParse(decoder.get());
     }
     ASSERT_EQ(parseResult, AVIF_RESULT_OK);

     // Decoding is incremental.
     uint32_t previouslyDecodedRowCount = 0;
     avifResult nextImageResult = useNthImageApi ? avifDecoderNthImage(decoder.get(), 0) : avifDecoderNextImage(decoder.get());
     while (nextImageResult == AVIF_RESULT_WAITING_ON_IO) {
         ASSERT_LT(data.available.size, data.fullSize)
             << (useNthImageApi ? "avifDecoderNthImage(0)" : "avifDecoderNextImage()") << " returned WAITING_ON_IO instead of OK";
         const uint32_t decodedRowCount = avifDecoderDecodedRowCount(decoder.get());
         ASSERT_GE(decodedRowCount, previouslyDecodedRowCount);
         const uint32_t minDecodedRowCount =
             getMinDecodedRowCount(reference.height, cellHeight, reference.alphaPlane != nullptr, data.available.size, data.fullSize);
         ASSERT_GE(decodedRowCount, minDecodedRowCount);
         comparePartialYUVA(reference, *decoder->image, decodedRowCount);

         previouslyDecodedRowCount = decodedRowCount;
         data.available.size = data.available.size + 1;
         nextImageResult = useNthImageApi ? avifDecoderNthImage(decoder.get(), 0) : avifDecoderNextImage(decoder.get());
     }
     ASSERT_EQ(nextImageResult, AVIF_RESULT_OK);
     ASSERT_EQ(data.available.size, data.fullSize);
     ASSERT_EQ(avifDecoderDecodedRowCount(decoder.get()), decoder->image->height);

     comparePartialYUVA(reference, *decoder->image, reference.height);
 }

 void decodeNonIncrementallyAndIncrementally(const avifRWData & encodedAvif, bool isPersistent, bool giveSizeHint, bool useNthImageApi, uint32_t cellHeight)
 {
     avifImagePtr reference(avifImageCreateEmpty(), avifImageDestroy);
     ASSERT_NE(reference, nullptr);
     testutil::avifDecoderPtr decoder(avifDecoderCreate(), avifDecoderDestroy);
     ASSERT_NE(decoder, nullptr);
     ASSERT_EQ(avifDecoderReadMemory(decoder.get(), reference.get(), encodedAvif.data, encodedAvif.size), AVIF_RESULT_OK);

     decodeIncrementally(encodedAvif, isPersistent, giveSizeHint, useNthImageApi, *reference, cellHeight);
 }

 //------------------------------------------------------------------------------

 } // namespace testutil
 } // namespace libavif
	// Copyright 2022 Google LLC. All rights reserved.
	// SPDX-License-Identifier: BSD-2-Clause

	#include "avif/avif.h"

	#include <algorithm>
	#include <vector>

	#include "avifincrtest_helpers.h"
	#include "aviftest_helpers.h"
	#include "gtest/gtest.h"

	namespace libavif
	{
	namespace testutil
	{
	namespace
	{

	//------------------------------------------------------------------------------

	// Verifies that the first (top) rowCount rows of image1 and image2 are identical.
	void comparePartialYUVA(const avifImage & image1, const avifImage & image2, uint32_t rowCount)
	{
	if (rowCount == 0) {
	return;
	}
	ASSERT_EQ(image1.width, image2.width);
	ASSERT_GE(image1.height, rowCount);
	ASSERT_GE(image2.height, rowCount);
	ASSERT_EQ(image1.depth, image2.depth);
	ASSERT_EQ(image1.yuvFormat, image2.yuvFormat);
	ASSERT_EQ(image1.yuvRange, image2.yuvRange);

	avifPixelFormatInfo info;
	avifGetPixelFormatInfo(image1.yuvFormat, &info);
	const uint32_t uvWidth = (image1.width + info.chromaShiftX) >> info.chromaShiftX;
	const uint32_t uvHeight = (rowCount + info.chromaShiftY) >> info.chromaShiftY;
	const uint32_t pixelByteCount = (image1.depth > 8) ? sizeof(uint16_t) : sizeof(uint8_t);

	for (uint32_t plane = 0; plane < (info.monochrome ? 1 : AVIF_PLANE_COUNT_YUV); ++plane) {
	const uint32_t width = (plane == AVIF_CHAN_Y) ? image1.width : uvWidth;
	const uint32_t widthByteCount = width * pixelByteCount;
	const uint32_t height = (plane == AVIF_CHAN_Y) ? rowCount : uvHeight;
	const uint8_t * data1 = image1.yuvPlanes[plane];
	const uint8_t * data2 = image2.yuvPlanes[plane];
	for (uint32_t y = 0; y < height; ++y) {
	ASSERT_TRUE(std::equal(data1, data1 + widthByteCount, data2));
	data1 += image1.yuvRowBytes[plane];
	data2 += image2.yuvRowBytes[plane];
	}
	}

	if (image1.alphaPlane) {
	ASSERT_NE(image2.alphaPlane, nullptr);
	ASSERT_EQ(image1.alphaPremultiplied, image2.alphaPremultiplied);
	const uint32_t widthByteCount = image1.width * pixelByteCount;
	const uint8_t * data1 = image1.alphaPlane;
	const uint8_t * data2 = image2.alphaPlane;
	for (uint32_t y = 0; y < rowCount; ++y) {
	ASSERT_TRUE(std::equal(data1, data1 + widthByteCount, data2));
	data1 += image1.alphaRowBytes;
	data2 += image2.alphaRowBytes;
	}
	}
	}

	// Returns the expected number of decoded rows when availableByteCount out of byteCount were
	// given to the decoder, for an image of height rows, split into cells of cellHeight rows.
	uint32_t getMinDecodedRowCount(uint32_t height, uint32_t cellHeight, bool hasAlpha, size_t availableByteCount, size_t byteCount)
	{
	// The whole image should be available when the full input is.
	if (availableByteCount >= byteCount) {
	return height;
	}
	// All but one cell should be decoded if at most 10 bytes are missing.
	if ((availableByteCount + 10) >= byteCount) {
	return height - cellHeight;
	}

	// Subtract the header because decoding it does not output any pixel.
	// Most AVIF headers are below 500 bytes.
	if (availableByteCount <= 500) {
	return 0;
	}
	availableByteCount -= 500;
	byteCount -= 500;
	// Alpha, if any, is assumed to be located before the other planes and to
	// represent at most 50% of the payload.
	if (hasAlpha) {
	if (availableByteCount <= (byteCount / 2)) {
	return 0;
	}
	availableByteCount -= byteCount / 2;
	byteCount -= byteCount / 2;
	}
	// Linearly map the input availability ratio to the decoded row ratio.
	const uint32_t minDecodedCellRowCount = (height / cellHeight) * availableByteCount / byteCount;
	const uint32_t minDecodedPxRowCount = minDecodedCellRowCount * cellHeight;
	// One cell is the incremental decoding granularity.
	// It is unlikely that bytes are evenly distributed among cells. Offset two of them.
	if (minDecodedPxRowCount <= (2 * cellHeight)) {
	return 0;
	}
	return minDecodedPxRowCount - 2 * cellHeight;
	}

	//------------------------------------------------------------------------------

	struct avifROPartialData
	{
	avifROData available;
	size_t fullSize;
	};

	// Implementation of avifIOReadFunc simulating a stream from an array. See avifIOReadFunc documentation.
	// io->data is expected to point to avifROPartialData.
	avifResult avifIOPartialRead(struct avifIO * io, uint32_t readFlags, uint64_t offset, size_t size, avifROData * out)
	{
	const avifROPartialData * data = (avifROPartialData *)io->data;
	if ((readFlags != 0) \|\| !data \|\| (data->fullSize < offset)) {
	return AVIF_RESULT_IO_ERROR;
	}
	if (data->fullSize < (offset + size)) {
	size = data->fullSize - offset;
	}
	if (data->available.size < (offset + size)) {
	return AVIF_RESULT_WAITING_ON_IO;
	}
	out->data = data->available.data + offset;
	out->size = size;
	return AVIF_RESULT_OK;
	}

	//------------------------------------------------------------------------------

	// Encodes the image as a grid of at most gridCols*gridRows cells.
	// The cell count is reduced to fit libavif or AVIF format constraints. If impossible, the encoded output is returned empty.
	// The final cellWidth and cellHeight are output.
	void encodeAsGrid(const avifImage & image, uint32_t gridCols, uint32_t gridRows, avifRWData * output, uint32_t * cellWidth, uint32_t * cellHeight)
	{
	// Chroma subsampling requires even dimensions. See ISO 23000-22 - 7.3.11.4.2
	const bool needEvenWidths = ((image.yuvFormat == AVIF_PIXEL_FORMAT_YUV420) \|\| (image.yuvFormat == AVIF_PIXEL_FORMAT_YUV422));
	const bool needEvenHeights = (image.yuvFormat == AVIF_PIXEL_FORMAT_YUV420);

	ASSERT_GT(gridCols * gridRows, 0u);
	*cellWidth = image.width / gridCols;
	*cellHeight = image.height / gridRows;

	// avifEncoderAddImageGrid() only accepts grids that evenly split the image into cells at least 64 pixels wide and tall.
	while ((gridCols > 1) &&
	(((cellWidth gridCols) != image.width) \|\| (cellWidth < 64) \|\| (needEvenWidths && ((cellWidth & 1) != 0)))) {
	--gridCols;
	*cellWidth = image.width / gridCols;
	}
	while ((gridRows > 1) &&
	(((cellHeight gridRows) != image.height) \|\| (cellHeight < 64) \|\| (needEvenHeights && ((cellHeight & 1) != 0)))) {
	--gridRows;
	*cellHeight = image.height / gridRows;
	}

	std::vector<testutil::avifImagePtr> cellImages;
	cellImages.reserve(gridCols * gridRows);
	for (uint32_t row = 0, iCell = 0; row < gridRows; ++row) {
	for (uint32_t col = 0; col < gridCols; ++col, ++iCell) {
	avifCropRect cell;
	cell.x = col * *cellWidth;
	cell.y = row * *cellHeight;
	cell.width = ((cell.x + cellWidth) <= image.width) ? cellWidth : (image.width - cell.x);
	cell.height = ((cell.y + cellHeight) <= image.height) ? cellHeight : (image.height - cell.y);
	cellImages.emplace_back(avifImageCreateEmpty(), avifImageDestroy);
	ASSERT_NE(cellImages.back(), nullptr);
	ASSERT_EQ(avifImageSetViewRect(cellImages.back().get(), &image, &cell), AVIF_RESULT_OK);
	}
	}

	testutil::avifEncoderPtr encoder(avifEncoderCreate(), avifEncoderDestroy);
	ASSERT_NE(encoder, nullptr);
	encoder->speed = AVIF_SPEED_FASTEST;
	std::vector<avifImage *> cellImagePtrs(cellImages.size()); // Just here to match libavif API.
	for (size_t i = 0; i < cellImages.size(); ++i) {
	cellImagePtrs[i] = cellImages[i].get();
	}
	ASSERT_EQ(avifEncoderAddImageGrid(encoder.get(), gridCols, gridRows, cellImagePtrs.data(), AVIF_ADD_IMAGE_FLAG_SINGLE), AVIF_RESULT_OK);
	ASSERT_EQ(avifEncoderFinish(encoder.get(), output), AVIF_RESULT_OK);
	}

	// Encodes the image to be decoded incrementally.
	void encodeAsIncremental(const avifImage & image, bool flatCells, avifRWData * output, uint32_t * cellWidth, uint32_t * cellHeight)
	{
	const uint32_t gridCols = image.width / 64; // 64px is the min cell width.
	const uint32_t gridRows = flatCells ? 1 : (image.height / 64);
	encodeAsGrid(image, (gridCols > 1) ? gridCols : 1, (gridRows > 1) ? gridRows : 1, output, cellWidth, cellHeight);
	}

	} // namespace

	void encodeRectAsIncremental(const avifImage & image,
	uint32_t width,
	uint32_t height,
	bool createAlphaIfNone,
	bool flatCells,
	avifRWData * output,
	uint32_t * cellWidth,
	uint32_t * cellHeight)
	{
	avifImagePtr subImage(avifImageCreateEmpty(), avifImageDestroy);
	ASSERT_NE(subImage, nullptr);
	ASSERT_LE(width, image.width);
	ASSERT_LE(height, image.height);
	avifPixelFormatInfo info;
	avifGetPixelFormatInfo(image.yuvFormat, &info);
	const avifCropRect rect {
	/x=/((image.width - width) / 2) & ~info.chromaShiftX, /y=/((image.height - height) / 2) & ~info.chromaShiftX, width, height
	};
	ASSERT_EQ(avifImageSetViewRect(subImage.get(), &image, &rect), AVIF_RESULT_OK);
	if (createAlphaIfNone && !subImage->alphaPlane) {
	ASSERT_NE(image.yuvPlanes[AVIF_CHAN_Y], nullptr) << "No luma plane to simulate an alpha plane";
	subImage->alphaPlane = image.yuvPlanes[AVIF_CHAN_Y];
	subImage->alphaRowBytes = image.yuvRowBytes[AVIF_CHAN_Y];
	subImage->alphaPremultiplied = AVIF_FALSE;
	subImage->imageOwnsAlphaPlane = AVIF_FALSE;
	}
	encodeAsIncremental(*subImage, flatCells, output, cellWidth, cellHeight);
	}

	//------------------------------------------------------------------------------

	void decodeIncrementally(const avifRWData & encodedAvif,
	bool isPersistent,
	bool giveSizeHint,
	bool useNthImageApi,
	const avifImage & reference,
	uint32_t cellHeight)
	{
	// AVIF cells are at least 64 pixels tall.
	if (cellHeight != reference.height) {
	ASSERT_GE(cellHeight, 64u);
	}

	// Emulate a byte-by-byte stream.
	avifROPartialData data = { /available=/ { encodedAvif.data, 0 }, /fullSize=/encodedAvif.size };
	avifIO io = { /destroy=/nullptr, avifIOPartialRead,
	/write=/nullptr, giveSizeHint ? encodedAvif.size : 0,
	isPersistent, &data };

	testutil::avifDecoderPtr decoder(avifDecoderCreate(), avifDecoderDestroy);
	ASSERT_NE(decoder, nullptr);
	avifDecoderSetIO(decoder.get(), &io);
	decoder->allowIncremental = AVIF_TRUE;

	// Parsing is not incremental.
	avifResult parseResult = avifDecoderParse(decoder.get());
	while (parseResult == AVIF_RESULT_WAITING_ON_IO) {
	ASSERT_LT(data.available.size, data.fullSize) << "avifDecoderParse() returned WAITING_ON_IO instead of OK";
	data.available.size = data.available.size + 1;
	parseResult = avifDecoderParse(decoder.get());
	}
	ASSERT_EQ(parseResult, AVIF_RESULT_OK);

	// Decoding is incremental.
	uint32_t previouslyDecodedRowCount = 0;
	avifResult nextImageResult = useNthImageApi ? avifDecoderNthImage(decoder.get(), 0) : avifDecoderNextImage(decoder.get());
	while (nextImageResult == AVIF_RESULT_WAITING_ON_IO) {
	ASSERT_LT(data.available.size, data.fullSize)
	<< (useNthImageApi ? "avifDecoderNthImage(0)" : "avifDecoderNextImage()") << " returned WAITING_ON_IO instead of OK";
	const uint32_t decodedRowCount = avifDecoderDecodedRowCount(decoder.get());
	ASSERT_GE(decodedRowCount, previouslyDecodedRowCount);
	const uint32_t minDecodedRowCount =
	getMinDecodedRowCount(reference.height, cellHeight, reference.alphaPlane != nullptr, data.available.size, data.fullSize);
	ASSERT_GE(decodedRowCount, minDecodedRowCount);
	comparePartialYUVA(reference, *decoder->image, decodedRowCount);

	previouslyDecodedRowCount = decodedRowCount;
	data.available.size = data.available.size + 1;
	nextImageResult = useNthImageApi ? avifDecoderNthImage(decoder.get(), 0) : avifDecoderNextImage(decoder.get());
	}
	ASSERT_EQ(nextImageResult, AVIF_RESULT_OK);
	ASSERT_EQ(data.available.size, data.fullSize);
	ASSERT_EQ(avifDecoderDecodedRowCount(decoder.get()), decoder->image->height);

	comparePartialYUVA(reference, *decoder->image, reference.height);
	}

	void decodeNonIncrementallyAndIncrementally(const avifRWData & encodedAvif, bool isPersistent, bool giveSizeHint, bool useNthImageApi, uint32_t cellHeight)
	{
	avifImagePtr reference(avifImageCreateEmpty(), avifImageDestroy);
	ASSERT_NE(reference, nullptr);
	testutil::avifDecoderPtr decoder(avifDecoderCreate(), avifDecoderDestroy);
	ASSERT_NE(decoder, nullptr);
	ASSERT_EQ(avifDecoderReadMemory(decoder.get(), reference.get(), encodedAvif.data, encodedAvif.size), AVIF_RESULT_OK);

	decodeIncrementally(encodedAvif, isPersistent, giveSizeHint, useNthImageApi, *reference, cellHeight);
	}

	//------------------------------------------------------------------------------

	} // namespace testutil
	} // namespace libavif