ios - Metal API 不会绘制简单的三角形 后面是 WWDC2014 讲座

Question

我听过 WWDC2014 上关于如何使用 Metal API 的讲座，他们正在用一个简单的三角形创建“Hello world”应用程序。我期待在绿色背景上看到一个红色三角形。一切都很好，但三角形本身不存在，我不明白为什么。请帮忙!

这些线是 Metal 着色器:

struct Vertex
{
    float3 position;
};

struct VertexOut
{
    float4 position [[position]];
    float4 color;
};

vertex VertexOut myVertexShader(
                            device Vertex* vertexArray [[ buffer(0) ]],
                            unsigned int vid                 [[ vertex_id ]])
{
    VertexOut out;
    float3 pos = vertexArray[vid].position;
    out.position = float4(pos[0], pos[1], pos[2], 0.0);
    out.color    = float4(1.0, 0.0, 0.0, 1.0);
    return out;
}

fragment float4 myFragmentShader(VertexOut interpolated [[ stage_in ]])
{
    return interpolated.color;
}

这些是 View :

@implementation MyView

- (instancetype)initWithCoder:(NSCoder *)coder
{
    self = [super initWithCoder:coder];

    if(self)
    {
        _device = MTLCreateSystemDefaultDevice();
    }
    NSLog(@"MyView::initWithCoder called");
    return self;
}

+(id)layerClass
{
    return [CAMetalLayer class];
}

@end

这些是 View Controller :

static const float zcoord = 0.f;
static const float vertexArrayData[] =
{
     -0.3,   -0.5, zcoord,
     0.3,    -0.5, zcoord,
     0.f,    0.2, zcoord
};

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    MyView* view = (MyView*) self.view;

    id<MTLCommandQueue> queue = [view.device newCommandQueue];
    id<MTLBuffer> vertexArray = [view.device newBufferWithBytes:vertexArrayData
                                                         length:sizeof(vertexArrayData)
                                                        options:0];

    MTLRenderPipelineDescriptor* desc = [MTLRenderPipelineDescriptor new];
    id<MTLLibrary> lib = [view.device newDefaultLibrary];
    desc.vertexFunction = [lib newFunctionWithName:@"myVertexShader"];
    desc.fragmentFunction = [lib newFunctionWithName:@"myFragmentShader"];
    desc.colorAttachments[0].pixelFormat = MTLPixelFormatBGRA8Unorm;

    id<MTLRenderPipelineState> renderPipeline = [view.device newRenderPipelineStateWithDescriptor:desc error:nil];

    id<MTLCommandBuffer> commandBuffer = [queue commandBuffer];
    id<CAMetalDrawable> drawable = [(CAMetalLayer*)view.layer nextDrawable];

    MTLRenderPassDescriptor* renderDesc = [MTLRenderPassDescriptor new];
    renderDesc.colorAttachments[0].texture = drawable.texture;
    renderDesc.colorAttachments[0].loadAction = MTLLoadActionClear;
    renderDesc.colorAttachments[0].clearColor = MTLClearColorMake(0.0, 1.0, 0.0, 1.0);

    id<MTLRenderCommandEncoder> render = [commandBuffer renderCommandEncoderWithDescriptor:renderDesc];
    [render setRenderPipelineState:renderPipeline];
    [render setVertexBuffer:vertexArray offset:0 atIndex:0];
    [render drawPrimitives:MTLPrimitiveTypeTriangle vertexStart:0 vertexCount:3];
    [render endEncoding];

    [commandBuffer presentDrawable:drawable];

    [commandBuffer commit];
}

Answer 1

我明白了，伙计们。

问题出在这一行:

out.position = float4(pos[0], pos[1], pos[2], 0.0);

float4 的最后一个组成部分不应为零。 1.0 有所帮助。

问候