零. 前言
这是我在Metal系列进行探索的第三篇文章，本章主要会介绍透明通道的视频如何渲染到屏幕上中，在Metal与图形渲染二：透明图片的渲染已经将一张静态的透明通道图片渲染到屏幕上去了，那么，如果这不是一张图片，而是一个视频呢？
现在我们的素材是这样的：
需要按照上一章的逻辑，将他渲染到屏幕上，展示透明特效：
视频还需要加上额外的处理，让我们来看看怎么实现吧！
一. 视频格式与图片格式
作为呈现给用户的载体，视频和图片都有他自己的基础格式，图片是RGB，视频是YUV，我们前面采样用到的图片纹理就是根据RGB格式来采样的，那么，对于视频，我们也需要把他看成若干张图片的结合，再对这些图片进行采样和处理，这时候，需要我们先将YUV转换为RGB，再进行处理。
1. RGB数据
RGB 表示红（Red）、绿（Green）、蓝（Blue），也就是光的三原色，将它们以不同的比例叠加，可以产生不同的颜色。屏幕就是由红、绿、蓝三种发光的颜色小点组成的。
比如一张1080p的图片，代表着有 1920 * 1080 个像素点。如果采用 RGB 编码方式，每个像素点都有红、绿、蓝三个原色，其中每个原色占用 1 个字节，每个像素占用3个字节，则一张1080p的图片就占用 1920 * 1280 * 3 / 1024 / 1024 = 7.03125MB 存储空间。比如著名的BMP位图就是这样保存图片的（所谓的RGB888格式，或者24位位图格式）。
当然，我们手机所看到的一张图片不可能这么大，这是得益于前人研究的图片压缩算法，不然一亿像素的图片，一张就要占几百M..
2. YUV数据
YUV 编码采用了明亮度和色度表示每个像素的颜色。其中Y表示明亮度（Luminance、Luma），也就是灰阶值。U、V 表示色度（Chrominance 或 Chroma）。Y'UV是工程师希望在黑白基础结构中使用彩色电视时发明的。他们需要一种与黑白（B＆W）电视兼容的信号传输方法，同时又能增加色彩。亮度分量已经以黑白信号形式存在，于是他们添加了UV信号作为解决方案。
Y'代表亮度分量（亮度），U和V代表色度（颜色）分量；术语Y'UV，YUV，YCbCr，YPbPr等的范围有时是模棱两可和重叠的。历史上，术语YUV和Y'UV用于电视系统中颜色信息的特定模拟编码，而YCbCr用于颜色信息的数字编码，适用于视频和静止图像压缩和传输，例如MPEG和JPEG。如今，术语YUV在计算机行业中通常用于描述使用YCbCr编码的文件格式。本文也会将YUV视为YCbCr。
CbCr怎么表现颜色呢，看看下面一幅图就知道了：
Y用图片表示如下：
再用RGB和YUV各自的维度看看图片：
3. YUV的采样
既然图片有他的压缩方式，那么我们的视频自然也有自己的压缩方式，由于人类对UV信号并不是那么敏感，因此，我们在采样了Y分量之后，可以对UV分量酌情减少，以达到压缩大小的目的。
目前主流的YUV采样方式有：YUV4:4:4，YUV4:2:2，YUV4:2:0
YUV 4:4:4采样，每一个Y对应一组UV分量。
YUV 4:2:2采样，每两个Y共用一组UV分量。
YUV 4:2:0采样，每四个Y共用一组UV分量。
下图为YUYV的采样示例（YUV422中的一种），大概就可以了解YUV是怎么采样的了。
二. RGB与YUV的转换
如果需要将YUV转换为RGB，我们需要设置转换矩阵和对应的偏移，业界上已经有算好的矩阵，我们照样用就可以了，但我们还需要简单了解一下根据纹理的信息，选择对应的转换矩阵，下面介绍三种转换矩阵：
typedef struct {
matrix_float3x3 matrix;
vector_float3 offset;
} HobenConvertMatrix;
// BT.601
static const HobenConvertMatrix HobenYUVColorConversion601 = {
.matrix = {
.columns[0] = { 1.164, 1.164, 1.164, },
.columns[1] = { 0.000, -0.392, 2.017, },
.columns[2] = { 1.596, -0.813, 0.000, },
},
.offset = { -(16.0/255.0), -0.5, -0.5 },
};
// BT.601 Full Range
static const HobenConvertMatrix HobenYUVColorConversion601FullRange = {
.matrix = {
.columns[0] = { 1.000, 1.000, 1.000, },
.columns[1] = { 0.000, -0.343, 1.765, },
.columns[2] = { 1.400, -0.711, 0.000, },
},
.offset = { 0.0, -0.5, -0.5 },
};
// BT.709
static const HobenConvertMatrix HobenYUVColorConversion709 = {
.matrix = {
.columns[0] = { 1.164, 1.164, 1.164, },
.columns[1] = { 0.000, -0.213, 2.112, },
.columns[2] = { 1.793, -0.533, 0.000, },
},
.offset = { -(16.0/255.0), -0.5, -0.5 },
};
上述三种矩阵信息，我们可以看到两个要素：BT601还是BT709、如果是BT601的话是否为Full Range，下面简单介绍一下：
BT601是标清数字电视（SDTV）设置的标准，BT.709为高清数字电视（HDTV）的ITU标准，目前应用最广泛的应该是BT.709了。
fullRange和videoRange
在apple关于图像pixelformat的定义中有关于yuv格式的420v和420f的定义
kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange = '420v',
/* Bi-Planar Component Y'CbCr 8-bit 4:2:0, video-range (luma=[16,235] chroma=[16,240]). baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrBiPlanar struct */
kCVPixelFormatType_420YpCbCr8BiPlanarFullRange = '420f',
/* Bi-Planar Component Y'CbCr 8-bit 4:2:0, full-range (luma=[0,255] chroma=[1,255]). baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrBiPlanar struct *
Apple's sample code有对使用哪个矩阵的示范代码，我们可以通过以下代码获取到应该使用哪个矩阵：
OSType pixelFormatType = CVPixelBufferGetPixelFormatType(pixelBuffer);
BOOL isFullYUVRange = (pixelFormatType == kCVPixelFormatType_420YpCbCr8BiPlanarFullRange ? YES : NO);
CFTypeRef colorAttachments = CVBufferGetAttachment(pixelBuffer, kCVImageBufferYCbCrMatrixKey, NULL);
HobenConvertMatrix preferredConversion = HobenYUVColorConversion601FullRange;
if (colorAttachments != NULL) {
if (CFStringCompare(colorAttachments, kCVImageBufferYCbCrMatrix_ITU_R_601_4, kCFCompareCaseInsensitive) == kCFCompareEqualTo) {
if (isFullYUVRange) {
preferredConversion = HobenYUVColorConversion601FullRange;
} else {
preferredConversion = HobenYUVColorConversion601;
}
} else {
preferredConversion = HobenYUVColorConversion709;
}
} else {
if (isFullYUVRange) {
preferredConversion = HobenYUVColorConversion601FullRange;
} else {
preferredConversion = HobenYUVColorConversion601;
}
}
不过一般来说，用BT.709标准渲染的视频的已经占大多数了，其实可以默认用709矩阵了。。
三. 开始渲染视频
现在我们知道了YUV是怎么转换成RGB了，那现在我们就可以像上一章一样，先提取出视频每一帧的YUV，在渲染过程中，根据转换矩阵转换为纹理的RGB，最后进行采样即可：
由上图我们可以知道，我们需要先根据视频Reader去采集到CMSampleBufferRef，根据CMSampleBufferRef获取CVMetalTextureRef，然后再把它变成MTLTexture，最后传给GPU去渲染。当然，如果有缓存CVMetalTextureCacheRef，比起前一章直接用[self.texture replaceRegion:region mipmapLevel:0 withBytes:imageBytes bytesPerRow:image.size.width * 4]; 会大大提高渲染的性能。
1. 视频采集——获取CMSampleBufferRef
首先我们需要根据AVAssetReader去获取到AVAssetReaderTrackOutput，根据这个Output来获取到CMSampleBufferRef，由于这一章重点是讲视频渲染的过程，所以就略过了，具体播放流程可以Google一下。
2. Y纹理提取和UV纹理提取
我们根据CMSampleBufferRef获取到CVMetalTextureRef
- (CVMetalTextureRef)currentPixelBuffer {
CMSampleBufferRef movieSampleBuffer = [self.assetReader readBuffer];
CVMetalTextureRef pixelBuffer = CMSampleBufferGetImageBuffer(movieSampleBuffer);
return pixelBuffer;
}
根据CVMetalTextureRef，获取Y分量和UV分量的id <MTLTexture>类型的纹理。
注意，在 iOS 中，录制出来的 yuv 放到 CVPixelBufferRef 中，分成两个 plane。Y 数据独占一个 plane，planeIndex = 0, UV 数据共用一个 plane，planeIndex = 1。Y纹理对应的是R通道，UV纹理对应的是RG通道（这个和OpenGL不同，OpenGL对应的是RA通道）。
即Y纹理对应的pixelFormat为MTLPixelFormatR8Unorm，对应的planeIndex为0；
UV纹理对应的pixelFormat为MTLPixelFormatRG8Unorm，对应的planeIndex为1；
我们首先写出一个通用的CVMetalTextureRef转纹理的方法：
- (id <MTLTexture>)textureWithPixelBuffer:(CVMetalTextureRef)pixelBuffer pixelFormat:(MTLPixelFormat)pixelFormat planeIndex:(NSInteger)planeIndex {
id <MTLTexture> texture = nil;
size_t width = CVPixelBufferGetWidthOfPlane(pixelBuffer, planeIndex);
size_t height = CVPixelBufferGetHeightOfPlane(pixelBuffer, planeIndex);
CVMetalTextureRef textureRef = NULL;
CVReturn status = CVMetalTextureCacheCreateTextureFromImage(NULL, _textureCache, pixelBuffer, NULL, pixelFormat, width, height, planeIndex, &textureRef);
if (status == kCVReturnSuccess) {
texture = CVMetalTextureGetTexture(textureRef);
CFRelease(textureRef);
} else {
texture = nil;
}
return texture;
}
传入对应的参数得到Y纹理和UV纹理：
id <MTLTexture> textureY = [self textureWithPixelBuffer:pixelBuffer pixelFormat:MTLPixelFormatR8Unorm planeIndex:0];
id <MTLTexture> textureUV = [self textureWithPixelBuffer:pixelBuffer pixelFormat:MTLPixelFormatRG8Unorm planeIndex:1];
3. 转换矩阵的生成
在前面我们也提到过，可以根据CVMetalTextureRef获取到对应信息，从而知道该用哪个转换矩阵，由于转换矩阵也要作为参数传入.metal文件中，因此我们还需要获取其缓冲id <MTLBuffer>：
- (void)setupMatrixWithPixelBuffer:(CVMetalTextureRef)pixelBuffer { // 设置好转换的矩阵
if (self.convertMatrix) {
return;
}
OSType pixelFormatType = CVPixelBufferGetPixelFormatType(pixelBuffer);
BOOL isFullYUVRange = (pixelFormatType == kCVPixelFormatType_420YpCbCr8BiPlanarFullRange ? YES : NO);
CFTypeRef colorAttachments = CVBufferGetAttachment(pixelBuffer, kCVImageBufferYCbCrMatrixKey, NULL);
HobenConvertMatrix preferredConversion = HobenYUVColorConversion601FullRange;
if (colorAttachments != NULL) {
if (CFStringCompare(colorAttachments, kCVImageBufferYCbCrMatrix_ITU_R_601_4, kCFCompareCaseInsensitive) == kCFCompareEqualTo) {
if (isFullYUVRange) {
preferredConversion = HobenYUVColorConversion601FullRange;
} else {
preferredConversion = HobenYUVColorConversion601;
}
} else {
preferredConversion = HobenYUVColorConversion709;
}
} else {
if (isFullYUVRange) {
preferredConversion = HobenYUVColorConversion601FullRange;
} else {
preferredConversion = HobenYUVColorConversion601;
}
}
self.convertMatrix = [self.mtkView.device newBufferWithBytes:&preferredConversion
length:sizeof(HobenConvertMatrix)
options:MTLResourceStorageModeShared];
}
4. 顶点的生成
这一步和之前渲染图形差不多，也是各取左半边和右半边的纹理，形成顶点映射，在此不赘述了，这里注意一下素材和上一章的不一样，这一次是左边提取alpha，右边提取rgb：
- (void)setupVertexWithRenderDesc:(MTLRenderPassDescriptor *)renderDesc {
if (self.rgbVertices && self.alphaVertices) {
return;
}
float heightScaling = 1.0;
float widthScaling = 1.0;
CGSize drawableSize = CGSizeMake(renderDesc.colorAttachments[0].texture.width, renderDesc.colorAttachments[0].texture.height);
CGRect bounds = CGRectMake(0, 0, drawableSize.width, drawableSize.height);
CGRect insetRect = AVMakeRectWithAspectRatioInsideRect(self.videoSize, bounds);
HobenRenderingResizingMode mode = CGSizeEqualToSize(self.videoSize, CGSizeZero) ? HobenRenderingResizingModeScale : HobenRenderingResizingModeAspectFill;
switch (mode) {
case HobenRenderingResizingModeScale:
heightScaling = 1.0;
widthScaling = 1.0;
break;
case HobenRenderingResizingModeAspectFit:
widthScaling = insetRect.size.width / drawableSize.width;
heightScaling = insetRect.size.height / drawableSize.height;
break;
case HobenRenderingResizingModeAspectFill:
widthScaling = drawableSize.height / insetRect.size.height;
heightScaling = drawableSize.width / insetRect.size.width;
break;
}
HobenVertex alphaVertices[] = {
// 顶点坐标 x, y, z, w --- 纹理坐标 x, y
{ {-widthScaling, heightScaling, 0.0, 1.0}, {0.0, 0.0} },
{ { widthScaling, heightScaling, 0.0, 1.0}, {0.5, 0.0} },
{ {-widthScaling, -heightScaling, 0.0, 1.0}, {0.0, 1.0} },
{ { widthScaling, -heightScaling, 0.0, 1.0}, {0.5, 1.0} },
};
CGFloat offset = .5f;
HobenVertex rgbVertices[] = {
// 顶点坐标 x, y, z, w --- 纹理坐标 x, y
{ {-widthScaling, heightScaling, 0.0, 1.0}, {0.0 + offset, 0.0} },
{ { widthScaling, heightScaling, 0.0, 1.0}, {0.5 + offset, 0.0} },
{ {-widthScaling, -heightScaling, 0.0, 1.0}, {0.0 + offset, 1.0} },
{ { widthScaling, -heightScaling, 0.0, 1.0}, {0.5 + offset, 1.0} },
};
self.rgbVertices = [_device newBufferWithBytes:rgbVertices length:sizeof(rgbVertices) options:MTLResourceStorageModeShared];
self.numVertices = sizeof(rgbVertices) / sizeof(HobenVertex);
self.alphaVertices = [_device newBufferWithBytes:alphaVertices length:sizeof(alphaVertices) options:MTLResourceStorageModeShared];
}
5. MSL编写
.metal文件中，我们实现的需求和之前差不多，都是需要左右各提取rgb和r，因此Metal结构和顶点着色器保持不变
typedef struct {
float4 vertexPosition [[ position ]]; // 顶点坐标
float2 textureCoorRgb; // 取RGB值的纹理坐标
float2 textureCoorAlpha; // 取Alpha值的纹理坐标
} RasterizerData;
vertex RasterizerData vertexShader(uint vertexId [[ vertex_id ]],
constant HobenVertex *rgbVertexArray [[ buffer(0) ]],
constant HobenVertex *alphaVertexArray [[ buffer(1) ]]) {
RasterizerData out;
out.vertexPosition = rgbVertexArray[vertexId].position;
out.textureCoorRgb = rgbVertexArray[vertexId].textureCoordinate;
out.textureCoorAlpha = alphaVertexArray[vertexId].textureCoordinate;
return out;
}
由于加入了Y纹理输入、UV纹理输入，还增加了转换矩阵的缓冲输入，因此片段着色器增加对应的输入通道，提取Y纹理的R通道，提取UV纹理的RG通道，并使用转换矩阵转换为RGB：
float3 rgbFromYuv(float2 textureCoor,
texture2d <float> textureY,
texture2d <float> textureUV,
constant HobenConvertMatrix *convertMatrix) {
constexpr sampler textureSampler (mag_filter::linear,
min_filter::linear);
float3 yuv = float3(textureY.sample(textureSampler, textureCoor).r,
textureUV.sample(textureSampler, textureCoor).rg);
return convertMatrix->matrix * (yuv + convertMatrix->offset);
}
由于我们需要分别提取Rgb和alpha，因此也是像上一章一样，这次分别调用Yuv转rgb方法提取：
fragment float4 fragmentShader(RasterizerData input [[ stage_in ]],
texture2d <float> textureY [[ texture(0) ]],
texture2d <float> textureUV [[ texture(1) ]],
constant HobenConvertMatrix *convertMatrix [[ buffer(0) ]]) {
float3 rgb = rgbFromYuv(input.textureCoorRgb, textureY, textureUV, convertMatrix);
float alpha = rgbFromYuv(input.textureCoorAlpha, textureY, textureUV, convertMatrix).r;
return float4(rgb, alpha);
}
在OC层再传入对应的数值即可：
- (void)drawInMTKView:(MTKView *)view {
id <MTLCommandBuffer> commandBuffer = [_commandQueue commandBuffer];
MTLRenderPassDescriptor *renderDesc = view.currentRenderPassDescriptor;
CVMetalTextureRef pixelBuffer = [self.dataSource currentPixelBuffer];
self.videoSize = CGSizeMake(CVPixelBufferGetWidth(pixelBuffer) / 2, CVPixelBufferGetHeight(pixelBuffer));
id <MTLTexture> textureY = [self textureWithPixelBuffer:pixelBuffer pixelFormat:MTLPixelFormatR8Unorm planeIndex:0];
id <MTLTexture> textureUV = [self textureWithPixelBuffer:pixelBuffer pixelFormat:MTLPixelFormatRG8Unorm planeIndex:1];
[self setupMatrixWithPixelBuffer:pixelBuffer];
if (pixelBuffer) {
CFRelease(pixelBuffer);
}
if (!renderDesc || !textureY || !textureUV) {
[commandBuffer commit];
return;
}
renderDesc.colorAttachments[0].clearColor = MTLClearColorMake(0, 0, 0, 0);
[self setupVertexWithRenderDesc:renderDesc];
id <MTLRenderCommandEncoder> commandEncoder = [commandBuffer renderCommandEncoderWithDescriptor:renderDesc];
[commandEncoder setViewport:(MTLViewport){0, 0, self.viewportSize.x, self.viewportSize.y, -1, 1}];
[commandEncoder setRenderPipelineState:self.pipelineState];
[commandEncoder setVertexBuffer:self.rgbVertices offset:0 atIndex:0];
[commandEncoder setVertexBuffer:self.alphaVertices offset:0 atIndex:1];
[commandEncoder setFragmentBuffer:self.convertMatrix offset:0 atIndex:0];
[commandEncoder setFragmentTexture:textureY atIndex:0];
[commandEncoder setFragmentTexture:textureUV atIndex:1];
[commandEncoder drawPrimitives:MTLPrimitiveTypeTriangleStrip vertexStart:0 vertexCount:self.numVertices];
[commandEncoder endEncoding];
[commandBuffer presentDrawable:view.currentDrawable];
[commandBuffer commit];
}
三. 总结
这篇文章主要介绍了视频和图片的区别，如何将视频的YUV转换成图片的RGB、转换的矩阵应该怎么选取，如何把视频的每一帧作为纹理渲染到屏幕中去。
下面这种图总结了怎么根据读取视频获得的CMSampleBufferRef一步步获得所需要纹理的RGB：
只要获取到RGB，我们就可以愉快地处理啦~下图介绍了怎么利用Yuv转rgb的思路，对输入的顶点进行采样处理，并作为片段着色器的输出（即采样左半边作为alpha、采样右半边作为rgb）
终于写了个需求相关的Demo出来啦~下一步想学习一下Metal的Debug和一些性能的反馈，研究一下和OpenGL相比的性能；还想钻研下MetalPetal大神级源码，还要继续加油呀！
附源码，这次按照苹果的建议对Metal的OC层进行了封装，Controller层一身轻松~
HobenMetalImageView：
//
// HobenMetalImageView.h
// HobenLearnMetal
//
// Created by Hoben on 2021/1/12.
//
#import <UIKit/UIKit.h>
@import MetalKit;
NS_ASSUME_NONNULL_BEGIN
typedef NS_ENUM(NSUInteger, HobenRenderingResizingMode) {
HobenRenderingResizingModeScale = 0,
HobenRenderingResizingModeAspectFit,
HobenRenderingResizingModeAspectFill,
};
@protocol HobenMetalImageViewDataSource <NSObject>
- (CVMetalTextureRef)currentPixelBuffer;
@end
@interface HobenMetalImageView : UIView
@property (nonatomic, assign) CVMetalTextureRef pixelBuffer;
@property (nonatomic, assign) CGSize videoSize;
@property (nonatomic, weak ) id <HobenMetalImageViewDataSource> dataSource;
@end
NS_ASSUME_NONNULL_END
//
// HobenMetalImageView.m
// HobenLearnMetal
//
// Created by Hoben on 2021/1/12.
//
#import "HobenMetalImageView.h"
#import <AVFoundation/AVFoundation.h>
#import "HobenShaderType.h"
// BT.601
static const HobenConvertMatrix HobenYUVColorConversion601 = {
.matrix = {
.columns[0] = { 1.164, 1.164, 1.164, },
.columns[1] = { 0.000, -0.392, 2.017, },
.columns[2] = { 1.596, -0.813, 0.000, },
},
.offset = { -(16.0/255.0), -0.5, -0.5 },
};
// BT.601 Full Range
static const HobenConvertMatrix HobenYUVColorConversion601FullRange = {
.matrix = {
.columns[0] = { 1.000, 1.000, 1.000, },
.columns[1] = { 0.000, -0.343, 1.765, },
.columns[2] = { 1.400, -0.711, 0.000, },
},
.offset = { 0.0, -0.5, -0.5 },
};
// BT.709
static const HobenConvertMatrix HobenYUVColorConversion709 = {
.matrix = {
.columns[0] = { 1.164, 1.164, 1.164, },
.columns[1] = { 0.000, -0.213, 2.112, },
.columns[2] = { 1.793, -0.533, 0.000, },
},
.offset = { -(16.0/255.0), -0.5, -0.5 },
};
@interface HobenMetalImageView () <MTKViewDelegate>
@property (nonatomic, strong) MTKView *mtkView;
@property (nonatomic, assign) vector_uint2 viewportSize;
@property (nonatomic, strong) id <MTLCommandQueue> commandQueue;
@property (nonatomic, strong) id <MTLDevice> device;
@property (nonatomic, strong) id <MTLRenderPipelineState> pipelineState;
@property (nonatomic, assign) CVMetalTextureCacheRef textureCache;
@property (nonatomic, strong) id <MTLBuffer> rgbVertices;
@property (nonatomic, strong) id <MTLBuffer> alphaVertices;
@property (nonatomic, strong) id<MTLBuffer> convertMatrix;
@property (nonatomic, assign) NSInteger numVertices;
@end
@implementation HobenMetalImageView
- (instancetype)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
[self setup];
}
return self;
}
- (void)setup {
[self setupMTKView];
[self setupCommandQueue];
[self setupPipeline];
}
- (void)setupMTKView {
self.mtkView = [[MTKView alloc] init];
_device = self.mtkView.device = MTLCreateSystemDefaultDevice();
self.mtkView.delegate = self;
self.mtkView.frame = self.bounds;
self.mtkView.opaque = NO;
[self addSubview:self.mtkView];
CVMetalTextureCacheCreate(NULL, NULL, _device, NULL, &_textureCache);
}
- (void)setupCommandQueue {
_commandQueue = [_device newCommandQueue];
}
- (void)setupPipeline {
id <MTLLibrary> defaultLibrary = [_device newDefaultLibrary];
id <MTLFunction> vertexFunc = [defaultLibrary newFunctionWithName:@"vertexShader"];
id <MTLFunction> fragmentFunc = [defaultLibrary newFunctionWithName:@"fragmentShader"];
MTLRenderPipelineDescriptor *pipelineDesc = [[MTLRenderPipelineDescriptor alloc] init];
pipelineDesc.colorAttachments[0].pixelFormat = self.mtkView.colorPixelFormat;
pipelineDesc.vertexFunction = vertexFunc;
pipelineDesc.fragmentFunction = fragmentFunc;
self.pipelineState = [_device newRenderPipelineStateWithDescriptor:pipelineDesc error:nil];
}
#pragma mark - MTKViewDelegate
- (void)mtkView:(MTKView *)view drawableSizeWillChange:(CGSize)size {
self.viewportSize = (vector_uint2){size.width, size.height};
}
- (void)drawInMTKView:(MTKView *)view {
id <MTLCommandBuffer> commandBuffer = [_commandQueue commandBuffer];
MTLRenderPassDescriptor *renderDesc = view.currentRenderPassDescriptor;
CVMetalTextureRef pixelBuffer = [self.dataSource currentPixelBuffer];
self.videoSize = CGSizeMake(CVPixelBufferGetWidth(pixelBuffer) / 2, CVPixelBufferGetHeight(pixelBuffer));
id <MTLTexture> textureY = [self textureWithPixelBuffer:pixelBuffer pixelFormat:MTLPixelFormatR8Unorm planeIndex:0];
id <MTLTexture> textureUV = [self textureWithPixelBuffer:pixelBuffer pixelFormat:MTLPixelFormatRG8Unorm planeIndex:1];
[self setupMatrixWithPixelBuffer:pixelBuffer];
if (pixelBuffer) {
CFRelease(pixelBuffer);
}
if (!renderDesc || !textureY || !textureUV) {
[commandBuffer commit];
return;
}
renderDesc.colorAttachments[0].clearColor = MTLClearColorMake(0, 0, 0, 0);
[self setupVertexWithRenderDesc:renderDesc];
id <MTLRenderCommandEncoder> commandEncoder = [commandBuffer renderCommandEncoderWithDescriptor:renderDesc];
[commandEncoder setViewport:(MTLViewport){0, 0, self.viewportSize.x, self.viewportSize.y, -1, 1}];
[commandEncoder setRenderPipelineState:self.pipelineState];
[commandEncoder setVertexBuffer:self.rgbVertices offset:0 atIndex:0];
[commandEncoder setVertexBuffer:self.alphaVertices offset:0 atIndex:1];
[commandEncoder setFragmentBuffer:self.convertMatrix offset:0 atIndex:0];
[commandEncoder setFragmentTexture:textureY atIndex:0];
[commandEncoder setFragmentTexture:textureUV atIndex:1];
[commandEncoder drawPrimitives:MTLPrimitiveTypeTriangleStrip vertexStart:0 vertexCount:self.numVertices];
[commandEncoder endEncoding];
[commandBuffer presentDrawable:view.currentDrawable];
[commandBuffer commit];
}
- (void)setupVertexWithRenderDesc:(MTLRenderPassDescriptor *)renderDesc {
if (self.rgbVertices && self.alphaVertices) {
return;
}
float heightScaling = 1.0;
float widthScaling = 1.0;
CGSize drawableSize = CGSizeMake(renderDesc.colorAttachments[0].texture.width, renderDesc.colorAttachments[0].texture.height);
CGRect bounds = CGRectMake(0, 0, drawableSize.width, drawableSize.height);
CGRect insetRect = AVMakeRectWithAspectRatioInsideRect(self.videoSize, bounds);
HobenRenderingResizingMode mode = CGSizeEqualToSize(self.videoSize, CGSizeZero) ? HobenRenderingResizingModeScale : HobenRenderingResizingModeAspectFill;
switch (mode) {
case HobenRenderingResizingModeScale:
heightScaling = 1.0;
widthScaling = 1.0;
break;
case HobenRenderingResizingModeAspectFit:
widthScaling = insetRect.size.width / drawableSize.width;
heightScaling = insetRect.size.height / drawableSize.height;
break;
case HobenRenderingResizingModeAspectFill:
widthScaling = drawableSize.height / insetRect.size.height;
heightScaling = drawableSize.width / insetRect.size.width;
break;
}
HobenVertex alphaVertices[] = {
// 顶点坐标 x, y, z, w --- 纹理坐标 x, y
{ {-widthScaling, heightScaling, 0.0, 1.0}, {0.0, 0.0} },
{ { widthScaling, heightScaling, 0.0, 1.0}, {0.5, 0.0} },
{ {-widthScaling, -heightScaling, 0.0, 1.0}, {0.0, 1.0} },
{ { widthScaling, -heightScaling, 0.0, 1.0}, {0.5, 1.0} },
};
CGFloat offset = .5f;
HobenVertex rgbVertices[] = {
// 顶点坐标 x, y, z, w --- 纹理坐标 x, y
{ {-widthScaling, heightScaling, 0.0, 1.0}, {0.0 + offset, 0.0} },
{ { widthScaling, heightScaling, 0.0, 1.0}, {0.5 + offset, 0.0} },
{ {-widthScaling, -heightScaling, 0.0, 1.0}, {0.0 + offset, 1.0} },
{ { widthScaling, -heightScaling, 0.0, 1.0}, {0.5 + offset, 1.0} },
};
self.rgbVertices = [_device newBufferWithBytes:rgbVertices length:sizeof(rgbVertices) options:MTLResourceStorageModeShared];
self.numVertices = sizeof(rgbVertices) / sizeof(HobenVertex);
self.alphaVertices = [_device newBufferWithBytes:alphaVertices length:sizeof(alphaVertices) options:MTLResourceStorageModeShared];
}
- (void)setupMatrixWithPixelBuffer:(CVMetalTextureRef)pixelBuffer { // 设置好转换的矩阵
if (self.convertMatrix) {
return;
}
OSType pixelFormatType = CVPixelBufferGetPixelFormatType(pixelBuffer);
BOOL isFullYUVRange = (pixelFormatType == kCVPixelFormatType_420YpCbCr8BiPlanarFullRange ? YES : NO);
CFTypeRef colorAttachments = CVBufferGetAttachment(pixelBuffer, kCVImageBufferYCbCrMatrixKey, NULL);
HobenConvertMatrix preferredConversion = HobenYUVColorConversion601FullRange;
if (colorAttachments != NULL) {
if (CFStringCompare(colorAttachments, kCVImageBufferYCbCrMatrix_ITU_R_601_4, kCFCompareCaseInsensitive) == kCFCompareEqualTo) {
if (isFullYUVRange) {
preferredConversion = HobenYUVColorConversion601FullRange;
} else {
preferredConversion = HobenYUVColorConversion601;
}
} else {
preferredConversion = HobenYUVColorConversion709;
}
} else {
if (isFullYUVRange) {
preferredConversion = HobenYUVColorConversion601FullRange;
} else {
preferredConversion = HobenYUVColorConversion601;
}
}
self.convertMatrix = [self.mtkView.device newBufferWithBytes:&preferredConversion
length:sizeof(HobenConvertMatrix)
options:MTLResourceStorageModeShared];
}
- (id <MTLTexture>)textureWithPixelBuffer:(CVMetalTextureRef)pixelBuffer pixelFormat:(MTLPixelFormat)pixelFormat planeIndex:(NSInteger)planeIndex {
id <MTLTexture> texture = nil;
size_t width = CVPixelBufferGetWidthOfPlane(pixelBuffer, planeIndex);
size_t height = CVPixelBufferGetHeightOfPlane(pixelBuffer, planeIndex);
CVMetalTextureRef textureRef = NULL;
CVReturn status = CVMetalTextureCacheCreateTextureFromImage(NULL, _textureCache, pixelBuffer, NULL, pixelFormat, width, height, planeIndex, &textureRef);
if (status == kCVReturnSuccess) {
texture = CVMetalTextureGetTexture(textureRef);
CFRelease(textureRef);
} else {
texture = nil;
}
return texture;
}
@end
HobenMetalImageController:
//
// ViewController.m
// HobenLearnMetal
//
// Created by Hoben on 2021/1/4.
//
#import "HobenMetalImageController.h"
#import "HobenShaderType.h"
#import "HobenMetalImageView.h"
#import "HobenAssetReader.h"
@interface HobenMetalImageController () <HobenMetalImageViewDataSource>
@property (nonatomic, strong) HobenMetalImageView *metalImageView;
@property (nonatomic, strong) HobenAssetReader *assetReader;
@end
@implementation HobenMetalImageController
- (void)viewDidLoad {
[super viewDidLoad];
self.view.backgroundColor = [UIColor grayColor];
self.metalImageView = [[HobenMetalImageView alloc] initWithFrame:self.view.bounds];
self.metalImageView.dataSource = self;
UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"tangseng"]];
imageView.frame = CGRectMake(0, 350, self.view.frame.size.width, 300);
[self.view addSubview:imageView];
[self.view addSubview:self.metalImageView];
NSURL *url = [[NSBundle mainBundle] URLForResource:@"flower" withExtension:@"mp4"];
self.assetReader = [[HobenAssetReader alloc] initWithUrl:url];
}
- (CVMetalTextureRef)currentPixelBuffer {
CMSampleBufferRef movieSampleBuffer = [self.assetReader readBuffer];
CVMetalTextureRef pixelBuffer = CMSampleBufferGetImageBuffer(movieSampleBuffer);
return pixelBuffer;
}
@end
HobenAssetReader：
//
// HobenAssetReader.m
// HobenLearnMetal
//
// Created by Hoben on 2021/1/12.
//
#import "HobenAssetReader.h"
@implementation HobenAssetReader
{
AVAssetReaderTrackOutput *readerVideoTrackOutput;
AVAssetReader *assetReader;
NSURL *videoUrl;
NSLock *lock;
}
- (instancetype)initWithUrl:(NSURL *)url {
self = [super init];
videoUrl = url;
lock = [[NSLock alloc] init];
[self customInit];
return self;
}
- (void)customInit {
NSDictionary *inputOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
AVURLAsset *inputAsset = [[AVURLAsset alloc] initWithURL:videoUrl options:inputOptions];
__weak typeof(self) weakSelf = self;
[inputAsset loadValuesAsynchronouslyForKeys:[NSArray arrayWithObject:@"tracks"] completionHandler: ^{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSError *error = nil;
AVKeyValueStatus tracksStatus = [inputAsset statusOfValueForKey:@"tracks" error:&error];
if (tracksStatus != AVKeyValueStatusLoaded)
{
NSLog(@"error %@", error);
return;
}
[weakSelf processWithAsset:inputAsset];
});
}];
}
- (void)processWithAsset:(AVAsset *)asset
{
[lock lock];
NSLog(@"processWithAsset");
NSError *error = nil;
assetReader = [AVAssetReader assetReaderWithAsset:asset error:&error];
NSMutableDictionary *outputSettings = [NSMutableDictionary dictionary];
[outputSettings setObject:@(kCVPixelFormatType_420YpCbCr8BiPlanarFullRange) forKey:(id)kCVPixelBufferPixelFormatTypeKey];
readerVideoTrackOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] outputSettings:outputSettings];
readerVideoTrackOutput.alwaysCopiesSampleData = NO;
[assetReader addOutput:readerVideoTrackOutput];
if ([assetReader startReading] == NO)
{
NSLog(@"Error reading from file at URL: %@", asset);
}
[lock unlock];
}
- (CMSampleBufferRef)readBuffer {
[lock lock];
CMSampleBufferRef sampleBufferRef = nil;
if (readerVideoTrackOutput) {
sampleBufferRef = [readerVideoTrackOutput copyNextSampleBuffer];
}
if (assetReader && assetReader.status == AVAssetReaderStatusCompleted) {
NSLog(@"customInit");
readerVideoTrackOutput = nil;
assetReader = nil;
[self customInit];
}
[lock unlock];
return sampleBufferRef;
}
@end
Shaders.metal：
//
// Shaders.metal
// HobenLearnMetal
//
// Created by Hoben on 2021/1/4.
//
#include <metal_stdlib>
#import "HobenShaderType.h"
using namespace metal;
typedef struct {
float4 vertexPosition [[ position ]]; // 顶点坐标
float2 textureCoorRgb; // 取RGB值的纹理坐标
float2 textureCoorAlpha; // 取Alpha值的纹理坐标
} RasterizerData;
vertex RasterizerData vertexShader(uint vertexId [[ vertex_id ]],
constant HobenVertex *rgbVertexArray [[ buffer(0) ]],
constant HobenVertex *alphaVertexArray [[ buffer(1) ]]) {
RasterizerData out;
out.vertexPosition = rgbVertexArray[vertexId].position;
out.textureCoorRgb = rgbVertexArray[vertexId].textureCoordinate;
out.textureCoorAlpha = alphaVertexArray[vertexId].textureCoordinate;
return out;
}
float3 rgbFromYuv(float2 textureCoor,
texture2d <float> textureY,
texture2d <float> textureUV,
constant HobenConvertMatrix *convertMatrix) {
constexpr sampler textureSampler (mag_filter::linear,
min_filter::linear);
float3 yuv = float3(textureY.sample(textureSampler, textureCoor).r,
textureUV.sample(textureSampler, textureCoor).rg);
return convertMatrix->matrix * (yuv + convertMatrix->offset);
}
fragment float4 fragmentShader(RasterizerData input [[ stage_in ]],
texture2d <float> textureY [[ texture(0) ]],
texture2d <float> textureUV [[ texture(1) ]],
constant HobenConvertMatrix *convertMatrix [[ buffer(0) ]]) {
float3 rgb = rgbFromYuv(input.textureCoorRgb, textureY, textureUV, convertMatrix);
float alpha = rgbFromYuv(input.textureCoorAlpha, textureY, textureUV, convertMatrix).r;
return float4(rgb, alpha);
}
//
// HobenShaderType.h
// HobenLearnMetal
//
// Created by Hoben on 2021/1/4.
//
#ifndef HobenShaderType_h
#define HobenShaderType_h
#include <simd/simd.h>
typedef struct {
vector_float4 position;
vector_float2 textureCoordinate;
} HobenVertex;
typedef struct {
matrix_float3x3 matrix;
vector_float3 offset;
} HobenConvertMatrix;
#endif /* HobenShaderType_h */
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