VK_VALIDATION_FEATURE_ENABLE_DEBUG_PRINTF_EXT

       在较新的vulkan版本中，添加了对debug_printf的支持，也就是说，现在可以在shader中打log了。

开启vulkan debug_printf

       debug_printf在vulkan中是VALIDATION_FEATURE，也就是说可以通过和其他验证层一样的方式来开启和关闭，非常方便。

注意，vulkan中开启debug_printf需要同时开启device扩展VK_KHR_SHADER_NON_SEMANTIC_INFO_EXTENSION_NAME

const std::vector<const char*> deviceExtensions = {
        ...
        VK_KHR_SHADER_NON_SEMANTIC_INFO_EXTENSION_NAME
		...
};

(推荐)使用Vulkan Configurator

       在最近的vulkan sdk中，新添加了名为Vulkan Configurator的工具，可以很方便的在UI界面下配置vulkan的validation layer

使用环境变量

       和vulkan旧版本相兼容，debug_printf也可以通过配置环境变量开启

VK_LAYER_ENABLES=VK_VALIDATION_FEATURE_ENABLE_DEBUG_PRINTF_EXT

       通过设置环境变量VK_LAYER_ENABLES到VK_VALIDATION_FEATURE_ENABLE_DEBUG_PRINTF_EXT来全局开启debug_printf功能

在代码中配置

       vulkan在代码中配置debug_printf会稍微复杂一些，但是可以对每个程序实现更精细的控制

const std::vector<VkValidationFeatureEnableEXT> enabledValidationLayers = {
        VK_VALIDATION_FEATURE_ENABLE_DEBUG_PRINTF_EXT
};

...

// debugPrintf
VkValidationFeaturesEXT validationFeatures{};
validationFeatures.sType = VK_STRUCTURE_TYPE_VALIDATION_FEATURES_EXT;
validationFeatures.pNext = nullptr;
validationFeatures.pEnabledValidationFeatures = enabledValidationLayers.data();
validationFeatures.enabledValidationFeatureCount = enabledValidationLayers.size();
validationFeatures.pDisabledValidationFeatures = nullptr;
validationFeatures.disabledValidationFeatureCount = 0;

...

instanceCreateInfo.pNext = &validationFeatures;

shader中打log

GLSL

#version 450
#extension GL_ARB_separate_shader_objects : enable
#extension GL_EXT_debug_printf : enable

layout(location = 0) in vec2 inPosition;
layout(location = 1) in vec3 inColor;

layout(location = 0) out vec3 fragColor;

void main() {
    gl_Position = vec4(inPosition, 0.0, 1.0);
    fragColor = inColor;

    // debugPrintfEXT
    if (gl_VertexIndex == 0)
    {
        float myfloat = 3.1415f;
        int foo = -135;

        debugPrintfEXT("Here are two float values %f, %f\n", 1.0, myfloat);

        debugPrintfEXT("Here's a smaller float value %1.2f\n", myfloat);

        debugPrintfEXT("Here's an integer %i with text before and after it\n", foo);

        foo = 256;
        debugPrintfEXT("Here's an integer in octal %o and hex 0x%x\n", foo, foo);

        foo = -135;
        debugPrintfEXT("%d is a negative integer\n", foo);

        vec4 floatvec = vec4(1.2f, 2.2f, 3.2f, 4.2f);
        debugPrintfEXT("Here's a vector of floats %1.2v4f\n", floatvec);

        debugPrintfEXT("Here's a float in sn %e\n", myfloat);

        debugPrintfEXT("Here's a float in sn %1.2e\n", myfloat);

        debugPrintfEXT("Here's a float in shortest %g\n", myfloat);

        debugPrintfEXT("Here's a float in hex %1.9a\n", myfloat);

        debugPrintfEXT("First printf with a %% and no value\n");

        debugPrintfEXT("Second printf with a value %i\n", foo);
    }
}

HLSL

struct VSInput
{
	float2 Position : POSITION;
	float3 Color : COLOR;
	uint vertId : SV_VertexID;
};

struct VSOutput
{
	float4 Position : SV_POSITION;
	float3 Color : COLOR;
};

const string first = "first string\n";
string second = "second string\n";

VSOutput vert(VSInput vin)
{
	VSOutput vout = (VSOutput)0;

	vout.Position = float4(vin.Position, 0.0, 1.0);
	vout.Color = vin.Color;

	if (vin.vertId == 0)
	{
		// CHECK:                OpExtension "SPV_KHR_non_semantic_info"
		// CHECK: [[set:%\d+]] = OpExtInstImport "NonSemantic.DebugPrintf"

		float myfloat = 3.1415f;
        int foo = -135;

        printf("Here are two float values %f, %f\n", 1.0, myfloat);

        printf("Here's a smaller float value %1.2f\n", myfloat);

        printf("Here's an integer %i with text before and after it\n", foo);

        foo = 256;
        printf("Here's an integer in octal %o and hex 0x%x\n", foo, foo);

        foo = -135;
        printf("%d is a negative integer\n", foo);

        float4 floatvec = float4(1.2f, 2.2f, 3.2f, 4.2f);
        printf("Here's a vector of floats %1.2v4f\n", floatvec);

        printf("Here's a float in sn %e\n", myfloat);

        printf("Here's a float in sn %1.2e\n", myfloat);

        printf("Here's a float in shortest %g\n", myfloat);

        printf("Here's a float in hex %1.9a\n", myfloat);

        printf("First printf with a %% and no value\n");

        printf("Second printf with a value %i\n", foo);
	}

	return vout;
}

float4 frag(VSOutput pin) : SV_TARGET
{
	return float4(pin.Color, 1.0);
}

GLSL中不要忘记#extension GL_EXT_debug_printf : enable,HLSL dxc编译器如果开启优化编译器会crash，现在如果要在hlsl打log，请先关闭优化

dxc -spirv -T vs_6_0 -E vert hlsl/shader.hlsl -Fo vert.spv -O0

最终效果

debug_printf