[Metal] テクスチャ（MTLTexture）を使う ref: http://qiita.com/edo_m18/items/6e44308d1b865e614f7c

defines-pixel-format

typedef enum : NSUInteger {
   MTLPixelFormatInvalid       = 0,
   /* Ordinary 8 bit formats */
   MTLPixelFormatA8Unorm       = 1,

   MTLPixelFormatR8Unorm       = 10,
   MTLPixelFormatR8Unorm_sRGB  = 11,
   MTLPixelFormatR8Snorm       = 12,
   MTLPixelFormatR8Uint        = 13,
   MTLPixelFormatR8Sint        = 14,
   /* Ordinary 16 bit formats */
   MTLPixelFormatR16Unorm      = 20,
   MTLPixelFormatR16Snorm      = 22,
   MTLPixelFormatR16Uint       = 23,
   MTLPixelFormatR16Sint       = 24,
   MTLPixelFormatR16Float      = 25,

   MTLPixelFormatRG8Unorm      = 30,
   MTLPixelFormatRG8Unorm_sRGB = 31,
   MTLPixelFormatRG8Snorm      = 32,
   MTLPixelFormatRG8Uint       = 33,
   MTLPixelFormatRG8Sint       = 34,
   /* Packed 16 bit formats */
   MTLPixelFormatB5G6R5Unorm      = 40,
   MTLPixelFormatA1BGR5Unorm      = 41,
   MTLPixelFormatABGR4Unorm       = 42,
   /* Ordinary 32 bit formats */
   MTLPixelFormatR32Uint          = 53,
   MTLPixelFormatR32Sint          = 54,
   MTLPixelFormatR32Float         = 55,

   MTLPixelFormatRG16Unorm        = 60,
   MTLPixelFormatRG16Snorm        = 62,
   MTLPixelFormatRG16Uint         = 63,
   MTLPixelFormatRG16Sint         = 64,
   MTLPixelFormatRG16Float        = 65,

   MTLPixelFormatRGBA8Unorm       = 70,
   MTLPixelFormatRGBA8Unorm_sRGB  = 71,
   MTLPixelFormatRGBA8Snorm       = 72,
   MTLPixelFormatRGBA8Uint        = 73,
   MTLPixelFormatRGBA8Sint        = 74,

   MTLPixelFormatBGRA8Unorm       = 80,
   MTLPixelFormatBGRA8Unorm_sRGB  = 81,
   /* Packed 32 bit formats */
   MTLPixelFormatRGB10A2Unorm     = 90,
   MTLPixelFormatRGB10A2Uint      = 91,
   MTLPixelFormatRG11B10Float     = 92,
   MTLPixelFormatRGB9E5Float      = 93,
   /* Ordinary 64 bit formats */
   MTLPixelFormatRG32Uint         = 103,
   MTLPixelFormatRG32Sint         = 104,
   MTLPixelFormatRG32Float        = 105,

   MTLPixelFormatRGBA16Unorm      = 110,
   MTLPixelFormatRGBA16Snorm      = 112,
   MTLPixelFormatRGBA16Uint       = 113,
   MTLPixelFormatRGBA16Sint       = 114,
   MTLPixelFormatRGBA16Float      = 115,
   /* Ordinary 128 bit formats */
   MTLPixelFormatRGBA32Uint       = 123,
   MTLPixelFormatRGBA32Sint       = 124,
   MTLPixelFormatRGBA32Float      = 125,
   /* Compressed formats. */
   /* PVRTC */
   MTLPixelFormatPVRTC_RGB_2BPP       = 160,
   MTLPixelFormatPVRTC_RGB_2BPP_sRGB  = 161,
   MTLPixelFormatPVRTC_RGB_4BPP       = 162,
   MTLPixelFormatPVRTC_RGB_4BPP_sRGB  = 163,
   MTLPixelFormatPVRTC_RGBA_2BPP      = 164,
   MTLPixelFormatPVRTC_RGBA_2BPP_sRGB = 165,
   MTLPixelFormatPVRTC_RGBA_4BPP      = 166,
   MTLPixelFormatPVRTC_RGBA_4BPP_sRGB = 167,
   /* ETC2 */
   MTLPixelFormatEAC_R11Unorm     = 170,
   MTLPixelFormatEAC_R11Snorm     = 172,
   MTLPixelFormatEAC_RG11Unorm    = 174,
   MTLPixelFormatEAC_RG11Snorm    = 176,
   MTLPixelFormatEAC_RGBA8        = 178,
   MTLPixelFormatEAC_RGBA8_sRGB   = 179,
   MTLPixelFormatETC2_RGB8        = 180,
   MTLPixelFormatETC2_RGB8_sRGB   = 181,
   MTLPixelFormatETC2_RGB8A1      = 182,
   MTLPixelFormatETC2_RGB8A1_sRGB = 183,

   MTLPixelFormatASTC_4x4_sRGB    = 186,
   MTLPixelFormatASTC_5x4_sRGB    = 187,
   MTLPixelFormatASTC_5x5_sRGB    = 188,
   MTLPixelFormatASTC_6x5_sRGB    = 189,
   MTLPixelFormatASTC_6x6_sRGB    = 190,
   MTLPixelFormatASTC_8x5_sRGB    = 192,
   MTLPixelFormatASTC_8x6_sRGB    = 193,
   MTLPixelFormatASTC_8x8_sRGB    = 194,
   MTLPixelFormatASTC_10x5_sRGB   = 195,
   MTLPixelFormatASTC_10x6_sRGB   = 196,
   MTLPixelFormatASTC_10x8_sRGB   = 197,
   MTLPixelFormatASTC_10x10_sRGB  = 198,
   MTLPixelFormatASTC_12x10_sRGB  = 199,
   MTLPixelFormatASTC_12x12_sRGB  = 200,

   MTLPixelFormatASTC_4x4_LDR     = 204,
   MTLPixelFormatASTC_5x4_LDR     = 205,
   MTLPixelFormatASTC_5x5_LDR     = 206,
   MTLPixelFormatASTC_6x5_LDR     = 207,
   MTLPixelFormatASTC_6x6_LDR     = 208,
   MTLPixelFormatASTC_8x5_LDR     = 210,
   MTLPixelFormatASTC_8x6_LDR     = 211,
   MTLPixelFormatASTC_8x8_LDR     = 212,
   MTLPixelFormatASTC_10x5_LDR    = 213,
   MTLPixelFormatASTC_10x6_LDR    = 214,
   MTLPixelFormatASTC_10x8_LDR    = 215,
   MTLPixelFormatASTC_10x10_LDR   = 216,
   MTLPixelFormatASTC_12x10_LDR   = 217,
   MTLPixelFormatASTC_12x12_LDR   = 218,

   MTLPixelFormatGBGR422          = 240,
   MTLPixelFormatBGRG422          = 241,

   MTLPixelFormatDepth32Float     = 252,
   MTLPixelFormatStencil8         = 253,
} MTLPixelFormat;

file0.m

// テクスチャ用画像を取得
UIImage *image = [UIImage imageNamed:@"hoge.jpg"];
CGImageRef imageRef = image.CGImage;

// サイズなど必要なデータを集める
NSUInteger width  = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);

// Color Space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

// 画像データ情報とメモリ割り当て
NSUInteger componentCount = 4;
uint8_t *rawData = (uint8_t*)calloc(width * height * coumponentCount, sizeof(uint8_t));
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow   = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;

// BitmapContextを生成
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, (CGBitmapInfo)(kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big));

// 画像を描画
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);

// 解放
CGColorSpaceRelease(colorSpace);
CGContextRelease(imageRef);

// MTLTextureDescriptorオブジェクトの生成。
// ピクセルフォーマット、幅、高さを指定する。
MTLTextureDescriptor *textureDescriptor = [MTLTextureDescriptor texture2DDescriptorWithPixelFormat:MTLPixelFormatRGBA8Unorm width:width height:height mipmapped:YES];

// テクスチャを生成
id <MTLTexture> texture = [device newTextureWithDescriptor:textureDescriptor];

// MTLRegionを生成。（3D空間の範囲も指定できるっぽいが、今回はテクスチャなので`2D`
MTLRegion region = MTLRegionMake2D(0, 0, width, height);

// 画像データをテクスチャに書き込む
[texture replaceRegion:region mipmapLevel:0 withBytes:rawData bytesPerRow:bytesPerRow];

file1.m

// MTLRenderPassDescriptorオブジェクトを生成
MTLRenderPassDescriptor *renderPassDescriptor = [MTLRenderPassDescriptor renderPassDescriptor];

// colorAttachmentsに上記で生成した`texture`を設定
renderPassDescriptor.colorAttachments[0].texture     = texture;

// このRender Passが実行されるときの挙動を設定
renderPassDescriptor.colorAttachments[0].loadAction  = MTLLoadActionClear;
renderPassDescriptor.colorAttachments[0].clearColor  = MTLClearColorMake(1.0, 0.0, 0.0, 1.0);
renderPassDescriptor.colorAttachments[0].storeAction = MTLStoreActionStore;

file2.m

MTLSamplerDescriptor *samplerDescriptor = [[MTLSamplerDescriptor alloc] init];
samplerDescriptor.minFilter = MTLSamplerMinMagFilterNearest;
samplerDescriptor.magFilter = MTLSamplerMinMagFilterLinear;
samplerDescriptor.sAddressMode = MTLSamplerAddressModeRepeat;
samplerDescriptor.tAddressMode = MTLSamplerAddressModeRepeat;

// `MTLSamplerState`を生成
self.sampler = [self.device newSamplerStateWithDescriptor:samplerDescriptor];

file3.m

// テクスチャを受け取って`MTLRenderPassDescriptor `を作るヘルパーメソッド
- (MTLRenderPassDescriptor *)createRenderPassDescriptorWithTexture:(id <MTLTexture>)texture
{
    MTLRenderPassDescriptor *renderPassDescriptor = [[MTLRenderPassDescriptor alloc] init];
    renderPassDescriptor.colorAttachments[0].texture     = texture;
    renderPassDescriptor.colorAttachments[0].loadAction  = MTLLoadActionClear;
    renderPassDescriptor.colorAttachments[0].clearColor  = MTLClearColorMake(0.0, 104.0/255.0, 5.0/255.0, 1.0);
    renderPassDescriptor.colorAttachments[0].storeAction = MTLStoreActionStore;

    return renderPassDescriptor;
}

file4.txt

fragment half4 video_fragment(VertexOut input [[stage_in]],
                              texture2d<float> tex2D [[texture(0)]]) {
    constexpr sampler s_quad(filter::linear);
    float4 color = tex2D.sample(s_quad, input.texCoord);
    return half4(color);
}