system/ulib/image-format/image_format.cpp - zircon/ - Git at Google

 // Copyright 2018 The Fuchsia Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "lib/image-format/image_format.h"

 #include <zircon/assert.h>

 #include <map>
 #include <set>

 namespace {

 // There are two aspects of the ColorSpace and PixelFormat that we care about:
 //   * bits-per-sample - bits per primary sample (R, G, B, or Y)
 //   * RGB vs. YUV - whether the system supports the ColorSpace or PixelFormat
 //     representing RGB data or YUV data.  Any given ColorSpace only supports
 //     one or the other. Currently any given PixelFormat only supports one or
 //     the other and this isn't likely to change.
 // While we could just list all the ColorSpace(s) that each PixelFormat could
 // plausibly support, expressing in terms of bits-per-sample and RGB vs. YUV is
 // perhaps easier to grok.

 enum ColorType {
     kColorType_NONE,
     kColorType_RGB,
     kColorType_YUV
 };

 struct SamplingInfo {
     std::set<uint32_t> possible_bits_per_sample;
     ColorType color_type;
 };

 const std::map<fuchsia_sysmem_ColorSpaceType, SamplingInfo> kColorSpaceSamplingInfo = {
     {fuchsia_sysmem_ColorSpaceType_SRGB, {{8, 10, 12, 16}, kColorType_RGB}},
     {fuchsia_sysmem_ColorSpaceType_REC601_NTSC, {{8, 10}, kColorType_YUV}},
     {fuchsia_sysmem_ColorSpaceType_REC601_NTSC_FULL_RANGE, {{8, 10}, kColorType_YUV}},
     {fuchsia_sysmem_ColorSpaceType_REC601_PAL, {{8, 10}, kColorType_YUV}},
     {fuchsia_sysmem_ColorSpaceType_REC601_PAL_FULL_RANGE, {{8, 10}, kColorType_YUV}},
     {fuchsia_sysmem_ColorSpaceType_REC709, {{8, 10}, kColorType_YUV}},
     {fuchsia_sysmem_ColorSpaceType_REC2020, {{10, 12}, kColorType_YUV}},
     {fuchsia_sysmem_ColorSpaceType_REC2100, {{10, 12}, kColorType_YUV}},
 };
 const std::map<fuchsia_sysmem_PixelFormatType, SamplingInfo> kPixelFormatSamplingInfo = {
     {fuchsia_sysmem_PixelFormatType_R8G8B8A8, {{8}, kColorType_RGB}},
     {fuchsia_sysmem_PixelFormatType_BGRA32, {{8}, kColorType_RGB}},
     {fuchsia_sysmem_PixelFormatType_I420, {{8}, kColorType_YUV}},
     {fuchsia_sysmem_PixelFormatType_M420, {{8}, kColorType_YUV}},
     {fuchsia_sysmem_PixelFormatType_NV12, {{8}, kColorType_YUV}},
     {fuchsia_sysmem_PixelFormatType_YUY2, {{8}, kColorType_YUV}},
     // 8 bits RGB when uncompressed - in this context, MJPEG is essentially
     // pretending to be uncompressed.
     {fuchsia_sysmem_PixelFormatType_MJPEG, {{8}, kColorType_RGB}},
 };

 }  // namespace

 bool ImageFormatIsPixelFormatEqual(const fuchsia_sysmem_PixelFormat& a, const fuchsia_sysmem_PixelFormat& b) {
     return
         a.type == b.type &&
         // !has_format_modifier is for consistency with making format_modifier
         // optional in future.
         a.has_format_modifier == b.has_format_modifier &&
         // Must be 0 if !has_format_modifier.
         a.format_modifier.value == b.format_modifier.value;
 }

 bool ImageFormatIsSupportedColorSpaceForPixelFormat(const fuchsia_sysmem_ColorSpace& color_space, const fuchsia_sysmem_PixelFormat& pixel_format) {
     // Not yet supported.
     ZX_DEBUG_ASSERT(!pixel_format.has_format_modifier);
     auto color_space_sampling_info_iter = kColorSpaceSamplingInfo.find(color_space.type);
     if (color_space_sampling_info_iter == kColorSpaceSamplingInfo.end()) {
         return false;
     }
     auto pixel_format_sampling_info_iter = kPixelFormatSamplingInfo.find(pixel_format.type);
     if (pixel_format_sampling_info_iter == kPixelFormatSamplingInfo.end()) {
         return false;
     }
     const SamplingInfo& color_space_sampling_info = color_space_sampling_info_iter->second;
     const SamplingInfo& pixel_format_sampling_info = pixel_format_sampling_info_iter->second;
     if (color_space_sampling_info.color_type != pixel_format_sampling_info.color_type) {
         return false;
     }
     bool is_bits_per_sample_match_found = false;
     for (uint32_t bits_per_sample : color_space_sampling_info.possible_bits_per_sample) {
         auto pixel_format_bits_per_sample_iter = pixel_format_sampling_info.possible_bits_per_sample.find(bits_per_sample);
         if (pixel_format_bits_per_sample_iter != pixel_format_sampling_info.possible_bits_per_sample.end()) {
             is_bits_per_sample_match_found = true;
             break;
         }
     }
     if (!is_bits_per_sample_match_found) {
         return false;
     }
     return true;
 }

 bool ImageFormatIsSupported(const fuchsia_sysmem_PixelFormat* pixel_format) {
     if (pixel_format->has_format_modifier) {
         return false;
     }
     switch (pixel_format->type) {
         case fuchsia_sysmem_PixelFormatType_INVALID:
         case fuchsia_sysmem_PixelFormatType_MJPEG:
             return false;
         case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
         case fuchsia_sysmem_PixelFormatType_BGRA32:
         case fuchsia_sysmem_PixelFormatType_I420:
         case fuchsia_sysmem_PixelFormatType_M420:
         case fuchsia_sysmem_PixelFormatType_NV12:
         case fuchsia_sysmem_PixelFormatType_YUY2:
             return true;
     }
     return false;
 }

 // Overall bits per pixel, across all pixel data in the whole image.
 uint32_t ImageFormatBitsPerPixel(const fuchsia_sysmem_PixelFormat* pixel_format) {
     ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
     switch (pixel_format->type) {
         case fuchsia_sysmem_PixelFormatType_INVALID:
         case fuchsia_sysmem_PixelFormatType_MJPEG:
             // impossible; checked previously.
             ZX_DEBUG_ASSERT(false);
             return 0u;
         case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
             return 4u * 8u;
         case fuchsia_sysmem_PixelFormatType_BGRA32:
             return 4u * 8u;
         case fuchsia_sysmem_PixelFormatType_I420:
             return 12u;
         case fuchsia_sysmem_PixelFormatType_M420:
             return 12u;
         case fuchsia_sysmem_PixelFormatType_NV12:
             return 12u;
         case fuchsia_sysmem_PixelFormatType_YUY2:
             return 2u * 8u;
     }
     ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
     return 0u;
 }

 uint32_t ImageFormatStrideBytesPerWidthPixel(
     const fuchsia_sysmem_PixelFormat* pixel_format) {
     ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
     switch (pixel_format->type) {
         case fuchsia_sysmem_PixelFormatType_INVALID:
         case fuchsia_sysmem_PixelFormatType_MJPEG:
             // impossible; checked previously.
             ZX_DEBUG_ASSERT(false);
             return 0u;
         case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
             return 4u;
         case fuchsia_sysmem_PixelFormatType_BGRA32:
             return 4u;
         case fuchsia_sysmem_PixelFormatType_I420:
             return 1u;
         case fuchsia_sysmem_PixelFormatType_M420:
             return 1u;
         case fuchsia_sysmem_PixelFormatType_NV12:
             return 1u;
         case fuchsia_sysmem_PixelFormatType_YUY2:
             return 2u;
     }
     ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
     return 0u;
 }

 uint64_t ImageFormatImageSize(const fuchsia_sysmem_ImageFormat_2* image_format) {
     ZX_DEBUG_ASSERT(ImageFormatIsSupported(&image_format->pixel_format));
     uint64_t coded_height = image_format->coded_height;
     uint64_t bytes_per_row = image_format->bytes_per_row;
     switch (image_format->pixel_format.type) {
         case fuchsia_sysmem_PixelFormatType_INVALID:
         case fuchsia_sysmem_PixelFormatType_MJPEG:
             // impossible; checked previously.
             ZX_DEBUG_ASSERT(false);
             return 0u;
         case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
         case fuchsia_sysmem_PixelFormatType_BGRA32:
             return coded_height * bytes_per_row;
         case fuchsia_sysmem_PixelFormatType_I420:
             return coded_height * bytes_per_row * 3 / 2;
         case fuchsia_sysmem_PixelFormatType_M420:
             return coded_height * bytes_per_row * 3 / 2;
         case fuchsia_sysmem_PixelFormatType_NV12:
             return coded_height * bytes_per_row * 3 / 2;
         case fuchsia_sysmem_PixelFormatType_YUY2:
             return coded_height * bytes_per_row;
     }
     ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(image_format->pixel_format.type));
     return 0u;
 }

 uint32_t ImageFormatCodedWidthMinDivisor(
     const fuchsia_sysmem_PixelFormat* pixel_format) {
     ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
     switch (pixel_format->type) {
         case fuchsia_sysmem_PixelFormatType_INVALID:
         case fuchsia_sysmem_PixelFormatType_MJPEG:
             // impossible; checked previously.
             ZX_DEBUG_ASSERT(false);
             return 0u;
         case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
             return 1u;
         case fuchsia_sysmem_PixelFormatType_BGRA32:
             return 1u;
         case fuchsia_sysmem_PixelFormatType_I420:
             return 2u;
         case fuchsia_sysmem_PixelFormatType_M420:
             return 2u;
         case fuchsia_sysmem_PixelFormatType_NV12:
             return 2u;
         case fuchsia_sysmem_PixelFormatType_YUY2:
             return 2u;
     }
     ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
     return 0u;
 }

 uint32_t ImageFormatCodedHeightMinDivisor(
     const fuchsia_sysmem_PixelFormat* pixel_format) {
     ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
     switch (pixel_format->type) {
         case fuchsia_sysmem_PixelFormatType_INVALID:
         case fuchsia_sysmem_PixelFormatType_MJPEG:
             // impossible; checked previously.
             ZX_DEBUG_ASSERT(false);
             return 0u;
         case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
             return 1u;
         case fuchsia_sysmem_PixelFormatType_BGRA32:
             return 1u;
         case fuchsia_sysmem_PixelFormatType_I420:
             return 2u;
         case fuchsia_sysmem_PixelFormatType_M420:
             return 2u;
         case fuchsia_sysmem_PixelFormatType_NV12:
             return 2u;
         case fuchsia_sysmem_PixelFormatType_YUY2:
             return 2u;
     }
     ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
     return 0u;
 }

 uint32_t ImageFormatSampleAlignment(
     const fuchsia_sysmem_PixelFormat* pixel_format) {
     ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
     switch (pixel_format->type) {
         case fuchsia_sysmem_PixelFormatType_INVALID:
         case fuchsia_sysmem_PixelFormatType_MJPEG:
             // impossible; checked previously.
             ZX_DEBUG_ASSERT(false);
             return 0u;
         case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
             return 4u;
         case fuchsia_sysmem_PixelFormatType_BGRA32:
             return 4u;
         case fuchsia_sysmem_PixelFormatType_I420:
             return 2u;
         case fuchsia_sysmem_PixelFormatType_M420:
             return 2u;
         case fuchsia_sysmem_PixelFormatType_NV12:
             return 2u;
         case fuchsia_sysmem_PixelFormatType_YUY2:
             return 2u;
     }
     ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
     return 0u;
 }
	// Copyright 2018 The Fuchsia Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "lib/image-format/image_format.h"

	#include <zircon/assert.h>

	#include <map>
	#include <set>

	namespace {

	// There are two aspects of the ColorSpace and PixelFormat that we care about:
	// * bits-per-sample - bits per primary sample (R, G, B, or Y)
	// * RGB vs. YUV - whether the system supports the ColorSpace or PixelFormat
	// representing RGB data or YUV data. Any given ColorSpace only supports
	// one or the other. Currently any given PixelFormat only supports one or
	// the other and this isn't likely to change.
	// While we could just list all the ColorSpace(s) that each PixelFormat could
	// plausibly support, expressing in terms of bits-per-sample and RGB vs. YUV is
	// perhaps easier to grok.

	enum ColorType {
	kColorType_NONE,
	kColorType_RGB,
	kColorType_YUV
	};

	struct SamplingInfo {
	std::set<uint32_t> possible_bits_per_sample;
	ColorType color_type;
	};

	const std::map<fuchsia_sysmem_ColorSpaceType, SamplingInfo> kColorSpaceSamplingInfo = {
	{fuchsia_sysmem_ColorSpaceType_SRGB, {{8, 10, 12, 16}, kColorType_RGB}},
	{fuchsia_sysmem_ColorSpaceType_REC601_NTSC, {{8, 10}, kColorType_YUV}},
	{fuchsia_sysmem_ColorSpaceType_REC601_NTSC_FULL_RANGE, {{8, 10}, kColorType_YUV}},
	{fuchsia_sysmem_ColorSpaceType_REC601_PAL, {{8, 10}, kColorType_YUV}},
	{fuchsia_sysmem_ColorSpaceType_REC601_PAL_FULL_RANGE, {{8, 10}, kColorType_YUV}},
	{fuchsia_sysmem_ColorSpaceType_REC709, {{8, 10}, kColorType_YUV}},
	{fuchsia_sysmem_ColorSpaceType_REC2020, {{10, 12}, kColorType_YUV}},
	{fuchsia_sysmem_ColorSpaceType_REC2100, {{10, 12}, kColorType_YUV}},
	};
	const std::map<fuchsia_sysmem_PixelFormatType, SamplingInfo> kPixelFormatSamplingInfo = {
	{fuchsia_sysmem_PixelFormatType_R8G8B8A8, {{8}, kColorType_RGB}},
	{fuchsia_sysmem_PixelFormatType_BGRA32, {{8}, kColorType_RGB}},
	{fuchsia_sysmem_PixelFormatType_I420, {{8}, kColorType_YUV}},
	{fuchsia_sysmem_PixelFormatType_M420, {{8}, kColorType_YUV}},
	{fuchsia_sysmem_PixelFormatType_NV12, {{8}, kColorType_YUV}},
	{fuchsia_sysmem_PixelFormatType_YUY2, {{8}, kColorType_YUV}},
	// 8 bits RGB when uncompressed - in this context, MJPEG is essentially
	// pretending to be uncompressed.
	{fuchsia_sysmem_PixelFormatType_MJPEG, {{8}, kColorType_RGB}},
	};

	} // namespace

	bool ImageFormatIsPixelFormatEqual(const fuchsia_sysmem_PixelFormat& a, const fuchsia_sysmem_PixelFormat& b) {
	return
	a.type == b.type &&
	// !has_format_modifier is for consistency with making format_modifier
	// optional in future.
	a.has_format_modifier == b.has_format_modifier &&
	// Must be 0 if !has_format_modifier.
	a.format_modifier.value == b.format_modifier.value;
	}

	bool ImageFormatIsSupportedColorSpaceForPixelFormat(const fuchsia_sysmem_ColorSpace& color_space, const fuchsia_sysmem_PixelFormat& pixel_format) {
	// Not yet supported.
	ZX_DEBUG_ASSERT(!pixel_format.has_format_modifier);
	auto color_space_sampling_info_iter = kColorSpaceSamplingInfo.find(color_space.type);
	if (color_space_sampling_info_iter == kColorSpaceSamplingInfo.end()) {
	return false;
	}
	auto pixel_format_sampling_info_iter = kPixelFormatSamplingInfo.find(pixel_format.type);
	if (pixel_format_sampling_info_iter == kPixelFormatSamplingInfo.end()) {
	return false;
	}
	const SamplingInfo& color_space_sampling_info = color_space_sampling_info_iter->second;
	const SamplingInfo& pixel_format_sampling_info = pixel_format_sampling_info_iter->second;
	if (color_space_sampling_info.color_type != pixel_format_sampling_info.color_type) {
	return false;
	}
	bool is_bits_per_sample_match_found = false;
	for (uint32_t bits_per_sample : color_space_sampling_info.possible_bits_per_sample) {
	auto pixel_format_bits_per_sample_iter = pixel_format_sampling_info.possible_bits_per_sample.find(bits_per_sample);
	if (pixel_format_bits_per_sample_iter != pixel_format_sampling_info.possible_bits_per_sample.end()) {
	is_bits_per_sample_match_found = true;
	break;
	}
	}
	if (!is_bits_per_sample_match_found) {
	return false;
	}
	return true;
	}

	bool ImageFormatIsSupported(const fuchsia_sysmem_PixelFormat* pixel_format) {
	if (pixel_format->has_format_modifier) {
	return false;
	}
	switch (pixel_format->type) {
	case fuchsia_sysmem_PixelFormatType_INVALID:
	case fuchsia_sysmem_PixelFormatType_MJPEG:
	return false;
	case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
	case fuchsia_sysmem_PixelFormatType_BGRA32:
	case fuchsia_sysmem_PixelFormatType_I420:
	case fuchsia_sysmem_PixelFormatType_M420:
	case fuchsia_sysmem_PixelFormatType_NV12:
	case fuchsia_sysmem_PixelFormatType_YUY2:
	return true;
	}
	return false;
	}

	// Overall bits per pixel, across all pixel data in the whole image.
	uint32_t ImageFormatBitsPerPixel(const fuchsia_sysmem_PixelFormat* pixel_format) {
	ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
	switch (pixel_format->type) {
	case fuchsia_sysmem_PixelFormatType_INVALID:
	case fuchsia_sysmem_PixelFormatType_MJPEG:
	// impossible; checked previously.
	ZX_DEBUG_ASSERT(false);
	return 0u;
	case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
	return 4u * 8u;
	case fuchsia_sysmem_PixelFormatType_BGRA32:
	return 4u * 8u;
	case fuchsia_sysmem_PixelFormatType_I420:
	return 12u;
	case fuchsia_sysmem_PixelFormatType_M420:
	return 12u;
	case fuchsia_sysmem_PixelFormatType_NV12:
	return 12u;
	case fuchsia_sysmem_PixelFormatType_YUY2:
	return 2u * 8u;
	}
	ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
	return 0u;
	}

	uint32_t ImageFormatStrideBytesPerWidthPixel(
	const fuchsia_sysmem_PixelFormat* pixel_format) {
	ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
	switch (pixel_format->type) {
	case fuchsia_sysmem_PixelFormatType_INVALID:
	case fuchsia_sysmem_PixelFormatType_MJPEG:
	// impossible; checked previously.
	ZX_DEBUG_ASSERT(false);
	return 0u;
	case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
	return 4u;
	case fuchsia_sysmem_PixelFormatType_BGRA32:
	return 4u;
	case fuchsia_sysmem_PixelFormatType_I420:
	return 1u;
	case fuchsia_sysmem_PixelFormatType_M420:
	return 1u;
	case fuchsia_sysmem_PixelFormatType_NV12:
	return 1u;
	case fuchsia_sysmem_PixelFormatType_YUY2:
	return 2u;
	}
	ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
	return 0u;
	}

	uint64_t ImageFormatImageSize(const fuchsia_sysmem_ImageFormat_2* image_format) {
	ZX_DEBUG_ASSERT(ImageFormatIsSupported(&image_format->pixel_format));
	uint64_t coded_height = image_format->coded_height;
	uint64_t bytes_per_row = image_format->bytes_per_row;
	switch (image_format->pixel_format.type) {
	case fuchsia_sysmem_PixelFormatType_INVALID:
	case fuchsia_sysmem_PixelFormatType_MJPEG:
	// impossible; checked previously.
	ZX_DEBUG_ASSERT(false);
	return 0u;
	case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
	case fuchsia_sysmem_PixelFormatType_BGRA32:
	return coded_height * bytes_per_row;
	case fuchsia_sysmem_PixelFormatType_I420:
	return coded_height * bytes_per_row * 3 / 2;
	case fuchsia_sysmem_PixelFormatType_M420:
	return coded_height * bytes_per_row * 3 / 2;
	case fuchsia_sysmem_PixelFormatType_NV12:
	return coded_height * bytes_per_row * 3 / 2;
	case fuchsia_sysmem_PixelFormatType_YUY2:
	return coded_height * bytes_per_row;
	}
	ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(image_format->pixel_format.type));
	return 0u;
	}

	uint32_t ImageFormatCodedWidthMinDivisor(
	const fuchsia_sysmem_PixelFormat* pixel_format) {
	ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
	switch (pixel_format->type) {
	case fuchsia_sysmem_PixelFormatType_INVALID:
	case fuchsia_sysmem_PixelFormatType_MJPEG:
	// impossible; checked previously.
	ZX_DEBUG_ASSERT(false);
	return 0u;
	case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
	return 1u;
	case fuchsia_sysmem_PixelFormatType_BGRA32:
	return 1u;
	case fuchsia_sysmem_PixelFormatType_I420:
	return 2u;
	case fuchsia_sysmem_PixelFormatType_M420:
	return 2u;
	case fuchsia_sysmem_PixelFormatType_NV12:
	return 2u;
	case fuchsia_sysmem_PixelFormatType_YUY2:
	return 2u;
	}
	ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
	return 0u;
	}

	uint32_t ImageFormatCodedHeightMinDivisor(
	const fuchsia_sysmem_PixelFormat* pixel_format) {
	ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
	switch (pixel_format->type) {
	case fuchsia_sysmem_PixelFormatType_INVALID:
	case fuchsia_sysmem_PixelFormatType_MJPEG:
	// impossible; checked previously.
	ZX_DEBUG_ASSERT(false);
	return 0u;
	case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
	return 1u;
	case fuchsia_sysmem_PixelFormatType_BGRA32:
	return 1u;
	case fuchsia_sysmem_PixelFormatType_I420:
	return 2u;
	case fuchsia_sysmem_PixelFormatType_M420:
	return 2u;
	case fuchsia_sysmem_PixelFormatType_NV12:
	return 2u;
	case fuchsia_sysmem_PixelFormatType_YUY2:
	return 2u;
	}
	ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
	return 0u;
	}

	uint32_t ImageFormatSampleAlignment(
	const fuchsia_sysmem_PixelFormat* pixel_format) {
	ZX_DEBUG_ASSERT(ImageFormatIsSupported(pixel_format));
	switch (pixel_format->type) {
	case fuchsia_sysmem_PixelFormatType_INVALID:
	case fuchsia_sysmem_PixelFormatType_MJPEG:
	// impossible; checked previously.
	ZX_DEBUG_ASSERT(false);
	return 0u;
	case fuchsia_sysmem_PixelFormatType_R8G8B8A8:
	return 4u;
	case fuchsia_sysmem_PixelFormatType_BGRA32:
	return 4u;
	case fuchsia_sysmem_PixelFormatType_I420:
	return 2u;
	case fuchsia_sysmem_PixelFormatType_M420:
	return 2u;
	case fuchsia_sysmem_PixelFormatType_NV12:
	return 2u;
	case fuchsia_sysmem_PixelFormatType_YUY2:
	return 2u;
	}
	ZX_PANIC("Unknown Pixel Format: %d", static_cast<int>(pixel_format->type));
	return 0u;
	}