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BUG=chromium:587193

Review URL: https://codereview.chromium.org/1703653002 .

README.md

+**libyuv** is an open source project that includes YUV scaling and conversion functionality.
+
+* Scale YUV to prepare content for compression, with point, bilinear or box filter.
+* Convert to YUV from webcam formats.
+* Convert from YUV to formats for rendering/effects.
+* Rotate by 90/180/270 degrees to adjust for mobile devices in portrait mode.
+* Optimized for SSE2/SSSE3/AVX2 on x86/x64.
+* Optimized for Neon on Arm.
+* Optimized for DSP R2 on Mips.
+
+### Development
+
+See [Getting started] [1] for instructions on how to get started developing.
+
+You can also browse the [docs directory] [2] for more documentation.
+
+[1]: docs/getting_started.md
+[2]: docs/

docs/environment_variables.md

+# Introduction
+
+For test purposes, environment variables can be set to control libyuv behavior.  These should only be used for testing, to narrow down bugs or to test performance.
+
+# CPU
+
+By default the cpu is detected and the most advanced form of SIMD is used.  But you can disable instruction sets selectively, or completely, falling back on C code.  Set the variable to 1 to disable the specified instruction set.
+
+    LIBYUV_DISABLE_ASM
+    LIBYUV_DISABLE_X86
+    LIBYUV_DISABLE_SSE2
+    LIBYUV_DISABLE_SSSE3
+    LIBYUV_DISABLE_SSE41
+    LIBYUV_DISABLE_SSE42
+    LIBYUV_DISABLE_AVX
+    LIBYUV_DISABLE_AVX2
+    LIBYUV_DISABLE_AVX3
+    LIBYUV_DISABLE_ERMS
+    LIBYUV_DISABLE_FMA3
+    LIBYUV_DISABLE_MIPS_DSPR2
+    LIBYUV_DISABLE_NEON
+
+# Test Width/Height/Repeat
+
+The unittests default to a small image (32x18) to run fast.  This can be set by environment variable to test a specific resolutions.
+You can also repeat the test a specified number of iterations, allowing benchmarking and profiling.
+
+    set LIBYUV_WIDTH=1280
+    set LIBYUV_HEIGHT=720
+    set LIBYUV_REPEAT=999
+    set LIBYUV_FLAGS=-1
+    set LIBYUV_CPU_INFO=-1

docs/formats.md

+# Introduction
+
+Formats (FOURCC) supported by libyuv are detailed here.
+
+# Core Formats
+
+There are 2 core formats supported by libyuv - I420 and ARGB.  All YUV formats can be converted to/from I420.  All RGB formats can be converted to/from ARGB.
+
+Filtering functions such as scaling and planar functions work on I420 and/or ARGB.
+
+# OSX Core Media Pixel Formats
+
+This is how OSX formats map to libyuv
+
+    enum {
+      kCMPixelFormat_32ARGB          = 32,      FOURCC_BGRA
+      kCMPixelFormat_32BGRA          = 'BGRA',  FOURCC_ARGB
+      kCMPixelFormat_24RGB           = 24,      FOURCC_RAW
+      kCMPixelFormat_16BE555         = 16,      Not supported.
+      kCMPixelFormat_16BE565         = 'B565',  Not supported.
+      kCMPixelFormat_16LE555         = 'L555',  FOURCC_RGBO
+      kCMPixelFormat_16LE565         = 'L565',  FOURCC_RGBP
+      kCMPixelFormat_16LE5551        = '5551',  FOURCC_RGBO
+      kCMPixelFormat_422YpCbCr8      = '2vuy',  FOURCC_UYVY
+      kCMPixelFormat_422YpCbCr8_yuvs = 'yuvs',  FOURCC_YUY2
+      kCMPixelFormat_444YpCbCr8      = 'v308',  FOURCC_I444 ?
+      kCMPixelFormat_4444YpCbCrA8    = 'v408',  Not supported.
+      kCMPixelFormat_422YpCbCr16     = 'v216',  Not supported.
+      kCMPixelFormat_422YpCbCr10     = 'v210',  FOURCC_V210 previously.  Removed now.
+      kCMPixelFormat_444YpCbCr10     = 'v410',  Not supported.
+      kCMPixelFormat_8IndexedGray_WhiteIsZero = 0x00000028,  Not supported.
+    };
+
+
+# FOURCC (Four Charactacter Code) List
+
+The following is extracted from video_common.h as a complete list of formats supported by libyuv.
+
+    enum FourCC {
+      // 9 Primary YUV formats: 5 planar, 2 biplanar, 2 packed.
+      FOURCC_I420 = FOURCC('I', '4', '2', '0'),
+      FOURCC_I422 = FOURCC('I', '4', '2', '2'),
+      FOURCC_I444 = FOURCC('I', '4', '4', '4'),
+      FOURCC_I411 = FOURCC('I', '4', '1', '1'),
+      FOURCC_I400 = FOURCC('I', '4', '0', '0'),
+      FOURCC_NV21 = FOURCC('N', 'V', '2', '1'),
+      FOURCC_NV12 = FOURCC('N', 'V', '1', '2'),
+      FOURCC_YUY2 = FOURCC('Y', 'U', 'Y', '2'),
+      FOURCC_UYVY = FOURCC('U', 'Y', 'V', 'Y'),
+
+      // 2 Secondary YUV formats: row biplanar.
+      FOURCC_M420 = FOURCC('M', '4', '2', '0'),
+      FOURCC_Q420 = FOURCC('Q', '4', '2', '0'),
+
+      // 9 Primary RGB formats: 4 32 bpp, 2 24 bpp, 3 16 bpp.
+      FOURCC_ARGB = FOURCC('A', 'R', 'G', 'B'),
+      FOURCC_BGRA = FOURCC('B', 'G', 'R', 'A'),
+      FOURCC_ABGR = FOURCC('A', 'B', 'G', 'R'),
+      FOURCC_24BG = FOURCC('2', '4', 'B', 'G'),
+      FOURCC_RAW  = FOURCC('r', 'a', 'w', ' '),
+      FOURCC_RGBA = FOURCC('R', 'G', 'B', 'A'),
+      FOURCC_RGBP = FOURCC('R', 'G', 'B', 'P'),  // rgb565 LE.
+      FOURCC_RGBO = FOURCC('R', 'G', 'B', 'O'),  // argb1555 LE.
+      FOURCC_R444 = FOURCC('R', '4', '4', '4'),  // argb4444 LE.
+
+      // 4 Secondary RGB formats: 4 Bayer Patterns.
+      FOURCC_RGGB = FOURCC('R', 'G', 'G', 'B'),
+      FOURCC_BGGR = FOURCC('B', 'G', 'G', 'R'),
+      FOURCC_GRBG = FOURCC('G', 'R', 'B', 'G'),
+      FOURCC_GBRG = FOURCC('G', 'B', 'R', 'G'),
+
+      // 1 Primary Compressed YUV format.
+      FOURCC_MJPG = FOURCC('M', 'J', 'P', 'G'),
+
+      // 5 Auxiliary YUV variations: 3 with U and V planes are swapped, 1 Alias.
+      FOURCC_YV12 = FOURCC('Y', 'V', '1', '2'),
+      FOURCC_YV16 = FOURCC('Y', 'V', '1', '6'),
+      FOURCC_YV24 = FOURCC('Y', 'V', '2', '4'),
+      FOURCC_YU12 = FOURCC('Y', 'U', '1', '2'),  // Linux version of I420.
+      FOURCC_J420 = FOURCC('J', '4', '2', '0'),
+      FOURCC_J400 = FOURCC('J', '4', '0', '0'),
+
+      // 14 Auxiliary aliases.  CanonicalFourCC() maps these to canonical fourcc.
+      FOURCC_IYUV = FOURCC('I', 'Y', 'U', 'V'),  // Alias for I420.
+      FOURCC_YU16 = FOURCC('Y', 'U', '1', '6'),  // Alias for I422.
+      FOURCC_YU24 = FOURCC('Y', 'U', '2', '4'),  // Alias for I444.
+      FOURCC_YUYV = FOURCC('Y', 'U', 'Y', 'V'),  // Alias for YUY2.
+      FOURCC_YUVS = FOURCC('y', 'u', 'v', 's'),  // Alias for YUY2 on Mac.
+      FOURCC_HDYC = FOURCC('H', 'D', 'Y', 'C'),  // Alias for UYVY.
+      FOURCC_2VUY = FOURCC('2', 'v', 'u', 'y'),  // Alias for UYVY on Mac.
+      FOURCC_JPEG = FOURCC('J', 'P', 'E', 'G'),  // Alias for MJPG.
+      FOURCC_DMB1 = FOURCC('d', 'm', 'b', '1'),  // Alias for MJPG on Mac.
+      FOURCC_BA81 = FOURCC('B', 'A', '8', '1'),  // Alias for BGGR.
+      FOURCC_RGB3 = FOURCC('R', 'G', 'B', '3'),  // Alias for RAW.
+      FOURCC_BGR3 = FOURCC('B', 'G', 'R', '3'),  // Alias for 24BG.
+      FOURCC_CM32 = FOURCC(0, 0, 0, 32),  // Alias for BGRA kCMPixelFormat_32ARGB
+      FOURCC_CM24 = FOURCC(0, 0, 0, 24),  // Alias for RAW kCMPixelFormat_24RGB
+      FOURCC_L555 = FOURCC('L', '5', '5', '5'),  // Alias for RGBO.
+      FOURCC_L565 = FOURCC('L', '5', '6', '5'),  // Alias for RGBP.
+      FOURCC_5551 = FOURCC('5', '5', '5', '1'),  // Alias for RGBO.
+
+      // 1 Auxiliary compressed YUV format set aside for capturer.
+      FOURCC_H264 = FOURCC('H', '2', '6', '4'),
+
+# The ARGB FOURCC
+
+There are 4 ARGB layouts - ARGB, BGRA, ABGR and RGBA.  ARGB is most common by far, used for screen formats, and windows webcam drivers.
+
+The fourcc describes the order of channels in a ***register***.
+
+A fourcc provided by capturer, can be thought of string, e.g. "ARGB".
+
+On little endian machines, as an int, this would have 'A' in the lowest byte.  The FOURCC macro reverses the order:
+
+    #define FOURCC(a, b, c, d) (((uint32)(a)) | ((uint32)(b) << 8) | ((uint32)(c) << 16) | ((uint32)(d) << 24))
+
+So the "ARGB" string, read as an uint32, is
+
+    FOURCC_ARGB = FOURCC('A', 'R', 'G', 'B')
+
+If you were to read ARGB pixels as uint32's, the alpha would be in the high byte, and the blue in the lowest byte.  In memory, these are stored little endian, so 'B' is first, then 'G', 'R' and 'A' last.
+
+When calling conversion functions, the names match the FOURCC, so in this case it would be I420ToARGB().
+
+All formats can be converted to/from ARGB.
+
+Most 'planar_functions' work on ARGB (e.g. ARGBBlend).
+
+Some are channel order agnostic (e.g. ARGBScale).
+
+Some functions are symmetric (e.g. ARGBToBGRA is the same as BGRAToARGB, so its a macro).
+
+ARGBBlend expects preattenuated ARGB. The R,G,B are premultiplied by alpha.  Other functions don't care.

docs/rotation.md

+# Introduction
+
+Rotation by multiplies of 90 degrees allows mobile devices to rotate webcams from landscape to portrait.  The higher level functions ConvertToI420 and ConvertToARGB allow rotation of any format.  Optimized functionality is supported for I420, ARGB, NV12 and NV21.
+
+# ConvertToI420
+
+    int ConvertToI420(const uint8* src_frame, size_t src_size,
+                      uint8* dst_y, int dst_stride_y,
+                      uint8* dst_u, int dst_stride_u,
+                      uint8* dst_v, int dst_stride_v,
+                      int crop_x, int crop_y,
+                      int src_width, int src_height,
+                      int crop_width, int crop_height,
+                      enum RotationMode rotation,
+                      uint32 format);
+
+This function crops, converts, and rotates.  You should think of it in that order.
+  * Crops the original image, which is src_width x src_height, to crop_width x crop_height.  At this point the image is still not rotated.
+  * Converts the cropped region to I420.  Supports inverted source for src_height negative.
+  * Rotates by 90, 180 or 270 degrees.
+The buffer the caller provides should account for rotation.  Be especially important to get stride of the destination correct.
+
+e.g.
+640 x 480 NV12 captured<br>
+Crop to 640 x 360<br>
+Rotate by 90 degrees to 360 x 640.<br>
+Caller passes stride of 360 for Y and 360 / 2 for U and V.<br>
+Caller passes crop_width of 640, crop_height of 360.<br>
+
+# ConvertToARGB
+
+    int ConvertToARGB(const uint8* src_frame, size_t src_size,
+                      uint8* dst_argb, int dst_stride_argb,
+                      int crop_x, int crop_y,
+                      int src_width, int src_height,
+                      int crop_width, int crop_height,
+                      enum RotationMode rotation,
+                      uint32 format);
+
+Same as I420, but implementation is less optimized - reads columns and writes rows, 16 bytes at a time.
+
+# I420Rotate
+
+    int I420Rotate(const uint8* src_y, int src_stride_y,
+                   const uint8* src_u, int src_stride_u,
+                   const uint8* src_v, int src_stride_v,
+                   uint8* dst_y, int dst_stride_y,
+                   uint8* dst_u, int dst_stride_u,
+                   uint8* dst_v, int dst_stride_v,
+                   int src_width, int src_height, enum RotationMode mode);
+
+Destination is rotated, so pass dst_stride_y etc that consider rotation.<br>
+Rotate by 180 can be done in place, but 90 and 270 can not.
+
+Implementation (Neon/SSE2) uses 8 x 8 block transpose, so best efficiency is with sizes and pointers that are aligned to 8.
+
+Cropping can be achieved by adjusting the src_y/u/v pointers and src_width, src_height.
+
+Lower level plane functions are provided, allowing other planar formats to be rotated.  (e.g. I444)
+
+For other planar YUV formats (I444, I422, I411, I400, NV16, NV24), the planar functions are exposed and can be called directly
+
+
+    // Rotate a plane by 0, 90, 180, or 270.
+    int RotatePlane(const uint8* src, int src_stride,
+                    uint8* dst, int dst_stride,
+                    int src_width, int src_height, enum RotationMode mode);
+
+# ARGBRotate
+
+    LIBYUV_API
+    int ARGBRotate(const uint8* src_argb, int src_stride_argb,
+                   uint8* dst_argb, int dst_stride_argb,
+                   int src_width, int src_height, enum RotationMode mode);
+
+Same as I420, but implementation is less optimized - reads columns and writes rows.
+
+Rotate by 90, or any angle, can be achieved using ARGBAffine.
+
+# Mirror - Horizontal Flip
+
+Mirror functions for horizontally flipping an image, which can be useful for 'self view' of a webcam.
+
+    int I420Mirror(const uint8* src_y, int src_stride_y,
+                   const uint8* src_u, int src_stride_u,
+                   const uint8* src_v, int src_stride_v,
+                   uint8* dst_y, int dst_stride_y,
+                   uint8* dst_u, int dst_stride_u,
+                   uint8* dst_v, int dst_stride_v,
+                   int width, int height);
+    int ARGBMirror(const uint8* src_argb, int src_stride_argb,
+                   uint8* dst_argb, int dst_stride_argb,
+                   int width, int height);
+
+Mirror functionality can also be achieved with the I420Scale and ARGBScale functions by passing negative width and/or height.
+
+# Invert - Vertical Flip
+
+Inverting can be achieved with almost any libyuv function by passing a negative source height.
+
+I420Mirror and ARGBMirror can also be used to rotate by 180 degrees by passing a negative height.
+
+