关于数学：Glsl Mod与Hlsl Fmod

Glsl mod vs Hlsl fmod

我已经在HLSL中实现了此问题中描述的螺旋GLSL着色器，但是结果并不相同。我认为这是因为我已将GLSL中的mod函数转换为HLSL中的fmod。我怀疑只有在fmod函数的输入中我们有负数时，才会出现此问题。

我尝试用对我所做的函数的调用替换对mod的调用，该函数执行GLSL文档中描述的功能，并且可以正常工作：

mod returns the value of x modulo y. This is computed as x - y * floor(x/y).

我使用的代替fmod的工作代码是：

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float mod(float x, float y)
{
return x - y * floor(x/y)
}

与GLSL mod相比，MSDN说HLSL fmod函数可以做到这一点：

The floating-point remainder is calculated such that x = i * y + f, where i is an integer, f has the same sign as x, and the absolute value of f is less than the absolute value of y.

我已经使用了HLSL到GLSL转换器，并且fmod函数被转换为mod。但是，我不知道是否可以假设mod转换为fmod。

问题

GLSL mod和HLSL fmod有什么区别？

如何将MSDN fmod的隐式描述转换为伪代码实现？

GLSL着色器

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uniform float time;
uniform vec2 resolution;
uniform vec2 aspect;

void main( void ) {
vec2 position = -aspect.xy + 2.0 * gl_FragCoord.xy / resolution.xy * aspect.xy;
float angle = 0.0 ;
float radius = length(position) ;
if (position.x != 0.0 && position.y != 0.0){
angle = degrees(atan(position.y,position.x)) ;
}
float amod = mod(angle+30.0*time-120.0*log(radius), 30.0) ;
if (amod<15.0){
gl_FragColor = vec4( 0.0, 0.0, 0.0, 1.0 );
} else{
gl_FragColor = vec4( 1.0, 1.0, 1.0, 1.0 );
}
}

HLSL着色器

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struct Psl_VertexShaderInput
{
float3 pos : POSITION;
};

struct Psl_VertexShaderOutput
{
float4 pos : POSITION;

};

struct Psl_PixelShaderOutput
{
float4 Output0 : COLOR0;
};

float3 psl_positionOffset;
float2 psl_dimension;

Psl_VertexShaderOutput Psl_VertexShaderFunction(Psl_VertexShaderInput psl_input)
{
Psl_VertexShaderOutput psl_output = (Psl_VertexShaderOutput)0;

psl_output.pos = float4(psl_input.pos + psl_positionOffset, 1);

return psl_output;
}

float time : TIME;
float2 resolution : DIMENSION;

Psl_PixelShaderOutput Psl_PixelShaderFunction(float2 pos : VPOS)
{
Psl_PixelShaderOutput psl_output = (Psl_PixelShaderOutput)0;

float2 aspect = float2(resolution.x / resolution.y, 1.0);
float2 position = -aspect.xy + 2.0 * pos.xy / resolution.xy * aspect.xy;
float angle = 0.0;
float radius = length(position);
if (position.x != 0.0 && position.y != 0.0)
{
angle = degrees(atan2(position.y, position.x));
}
float amod = fmod((angle + 30.0 * time - 120.0 * log(radius)), 30.0);
if (amod < 15.0)
{
psl_output.Output0 = float4(0.0, 0.0, 0.0, 1.0);
return psl_output;
}

else
{
psl_output.Output0 = float4(1.0, 1.0, 1.0, 1.0);
return psl_output;
}

}

technique Default
{
pass P0
{
VertexShader = compile vs_3_0 Psl_VertexShaderFunction();
PixelShader = compile ps_3_0 Psl_PixelShaderFunction();
}
}