c++ - 16位浮点数和GL_HALF_FLOAT

我正在寻找/编写一个16位浮点数的C++实现，以便与OpenGL顶点缓冲区(纹理坐标，法线等)一起使用。到目前为止，这是我的要求:

必须为16位(显然)。

必须能够使用GL_HALF_FLOAT上传到OpenGL顶点缓冲区。

必须能够表示超出-1.0-+1.0的数字(否则，我将只使用归一化的GL_SHORT)。

必须能够与正常的32位浮点数进行转换。

算术运算无所谓-我只关心存储。

速度不是主要问题，但正确性才是首要问题。

到目前为止，这是我要使用的界面:

class half
{
public:
    half(void) : data(0) {}
    half(const half& h) : data(h.data) {}
    half(const unsigned short& s) : data(s) {}
    half(const float& f) : data(fromFloat(f)) {}
    half(const double& d) : data(fromDouble(d)) {}

    inline operator const float() { return toFloat(data); }
    inline operator const double() { return toDouble(data); }

    inline const half operator=(const float& rhs) { data = fromFloat(rhs); return *this; }
    inline const half operator=(const double& rhs) { data = fromDouble(rhs); return *this; }

private:
    unsigned short data;

    static unsigned short fromFloat(float f);
    static float toFloat(short h);

    inline static unsigned short fromDouble(double d) { return fromFloat((float)d); }
    inline static double toDouble(short h) { return (double)toFloat(h); }
};

std::ostream& operator<<(std::ostream& os, half h) { os << (float)h; }
std::istream& operator>>(std::istream& is, half& h) { float f; is >> f; h = f; }

最终，该类的真正关键在于toFloat()和fromFloat()函数，这是我需要帮助的。我已经找到了很多16位浮点实现的示例，但是没有一个提到是否可以将它们上传到OpenGL。

将16位浮点上传到OpenGL时，我应该注意哪些问题？有没有专门解决这些问题的半 float 实现方案？

编辑:根据大众需求，这是我的顶点数据如何生成，上传和渲染的方式。

这是在WireCubeEntity类中定义数据的方式:

VertexHalf vertices[8] = {
        vec3(-1.0f, -1.0f, -1.0f),
        vec3(1.0f, -1.0f, -1.0f),
        vec3(1.0f, 1.0f, -1.0f),
        vec3(-1.0f, 1.0f, -1.0f),
        vec3(-1.0f, -1.0f, 1.0f),
        vec3(1.0f, -1.0f, 1.0f),
        vec3(1.0f, 1.0f, 1.0f),
        vec3(-1.0f, 1.0f, 1.0f)
    };

    unsigned char indices[24] = {
        0, 1,
        1, 2,
        2, 3,
        3, 0,
        4, 5,
        5, 6,
        6, 7,
        7, 4,
        0, 4,
        1, 5,
        2, 6,
        3, 7
    };

    va.load(GL_LINES, VF_BASICHALF, 8, vertices, GL_UNSIGNED_BYTE, 24, indices);

其中va是VertexArray的实例。 va.load定义为:

MappedBuffers VertexArray::load(GLenum primitive, VertexFormat vertexFormat, unsigned int vertexCount, void* vertices,
                                                  GLenum indexFormat, unsigned int indexCount, void* indices)
{
    MappedBuffers ret;

    /* Check for invalid primitive types */
    if (primitive > GL_TRIANGLE_FAN)
    {
        error("in VertexFormat::load():\n");
        errormore("Invalid enum '%i' passed to 'primitive'.\n", primitive);
        return ret;
    }

    /* Clean up existing data */
    clean();

    /* Set up Vertex Array Object */
    glGenVertexArrays(1, &vao);
    bindArray();

    /* Create Vertex Buffer Object */
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, vertexSize(vertexFormat) * vertexCount, vertices, GL_STATIC_DRAW);
    if (!vertices) ret.vmap = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);

    /* Save variables for later usage */
    prim = primitive;
    vformat = vertexFormat;
    vcount = vertexCount;

    /* If we've been given index data, handle it */
    if (indexSize(indexFormat) != 0)
    {
        glGenBuffers(1, &ibo);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, indexSize(indexFormat) * indexCount, indices, GL_STATIC_DRAW);
        if (!indices) ret.imap = glMapBuffer(GL_ELEMENT_ARRAY_BUFFER, GL_WRITE_ONLY);

        iformat = indexFormat;
        icount = indexCount;
    }

    /* Handle the vertex format */
    switch (vformat)
    {
    case VF_BASIC:
        /* VF_BASIC only has a position - a 3-component float vector */
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
        break;
    case VF_32:
        /* VF_32 has 3 components for position, 2 for texture coordinates, and 3 for a normal.
        Position is at offset 0, TextureCoordinate is at offset 12, and Normal is at offset 20 */
        glEnableVertexAttribArray(0);
        glEnableVertexAttribArray(1);
        glEnableVertexAttribArray(2);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, vertexSize(VF_32), (void*)0);
        glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, vertexSize(VF_32), (void*)12);
        glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, vertexSize(VF_32), (void*)20);
        break;
    case VF_BASICHALF:
        /* VF_BASICHALF is very similar to VF_BASIC, except using half-floats instead of floats. */
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 3, GL_HALF_FLOAT, GL_FALSE, 0, (void*)0);
        break;
    case VF_WITHTANGENTS:
        /* VF_WITHTANGENTS is similar to VF_32, but with additional components for a Tangent. */
        /* Tangent is at offset 32 */
        glEnableVertexAttribArray(0);
        glEnableVertexAttribArray(1);
        glEnableVertexAttribArray(2);
        glEnableVertexAttribArray(3);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, vertexSize(VF_WITHTANGENTS), (void*)0);
        glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, vertexSize(VF_WITHTANGENTS), (void*)12);
        glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, vertexSize(VF_WITHTANGENTS), (void*)20);
        glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, vertexSize(VF_WITHTANGENTS), (void*)32);
        break;
    default:
        error("In VertexFormat::load():\n");
        errormore("Invalid enum '%i' passed to vertexFormat.\n", (int)vformat);
        clean();
        return MappedBuffers();
    }

    /* Unbind the vertex array */
    unbindArray();

    if (vertices) ready = true;

    return ret;
}

我知道我的功能很繁重。 MappedBuffers只是一个包含2个指针的结构，因此，如果我将NULL数据传递到VertexArray::load()，则可以使用指针将数据直接从文件加载到缓冲区(可能是从另一个线程加载)。 vertexSize是一个函数，它返回我传入的任何一种顶点格式的sizeof()，或者返回0表示无效的格式。

VertexHalf结构为:

struct VertexHalf
{
    VertexHalf(void) {}
    VertexHalf(vec3 _pos) :x(_pos.x), y(_pos.y), z(_pos.z) {}
    VertexHalf(float _x, float _y, float _z) : x(_x), y(_y), z(_z) {}

    half x, y, z, padding;
};

最后，使用我们之前加载的VertexArray渲染数据:

void VertexArray::draw(void)
{
    if (ready == false)
        return;

    /* Bind our vertex array */
    bindArray();

    /* Draw it's contents */
    if (ibo == 0)
        glDrawArrays(prim, 0, vcount);
    else
        glDrawElements(prim, icount, iformat, NULL);

    unbindArray();
}

最佳答案

编辑:最明显的错误出现在您的VertexHalf结构中。您有填充元素。但是，当您指定glVertexAttribPointer时，请在跨步中指定一个0，表示该行已紧密打包。因此，您可以更改VertexHalf以删除填充，也可以将glVertexAttribPointer更改为8个字节。

我将以下类与DirectX一起使用，以支持float16，它可以完美运行。

Float16.h:

#ifndef THE__FLOAT_16_H_
#define THE__FLOAT_16_H_

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

extern short FloatToFloat16( float value );
extern float Float16ToFloat( short value );

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

class Float16
{
protected:
    short mValue;
public:
    Float16();
    Float16( float value );
    Float16( const Float16& value );

    operator float();
    operator float() const;

    friend Float16 operator + ( const Float16& val1, const Float16& val2 );
    friend Float16 operator - ( const Float16& val1, const Float16& val2 );
    friend Float16 operator * ( const Float16& val1, const Float16& val2 );
    friend Float16 operator / ( const Float16& val1, const Float16& val2 );

    Float16& operator =( const Float16& val );
    Float16& operator +=( const Float16& val );
    Float16& operator -=( const Float16& val );
    Float16& operator *=( const Float16& val );
    Float16& operator /=( const Float16& val );
    Float16& operator -();
};

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16::Float16()
{
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16::Float16( float value )
{
    mValue  = FloatToFloat16( value );
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16::Float16( const Float16 &value )
{
    mValue  = value.mValue;
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16::operator float()
{
    return Float16ToFloat( mValue );
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16::operator float() const
{
    return Float16ToFloat( mValue );
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16& Float16::operator =( const Float16& val )
{
    mValue  = val.mValue;
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16& Float16::operator +=( const Float16& val )
{
    *this   = *this + val;
    return *this;
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16& Float16::operator -=( const Float16& val )
{
    *this   = *this - val;
    return *this;

}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16& Float16::operator *=( const Float16& val )
{
    *this   = *this * val;
    return *this;
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16& Float16::operator /=( const Float16& val )
{
    *this   = *this / val;
    return *this;
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16& Float16::operator -()
{
    *this   = Float16( -(float)*this );
    return *this;
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/
/*+----+                                 Friends                                       +----+*/
/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16 operator + ( const Float16& val1, const Float16& val2 )
{
    return Float16( (float)val1 + (float)val2 );
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16 operator - ( const Float16& val1, const Float16& val2 )
{
    return Float16( (float)val1 - (float)val2 );
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16 operator * ( const Float16& val1, const Float16& val2 )
{
    return Float16( (float)val1 * (float)val2 );
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

inline Float16 operator / ( const Float16& val1, const Float16& val2 )
{
    return Float16( (float)val1 / (float)val2 );
}

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/


#endif

Float16.cpp:

#include "Types/Float16.h"

//#include <d3dx9.h>

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/

short FloatToFloat16( float value )
{
    short   fltInt16;
    int     fltInt32;
    memcpy( &fltInt32, &value, sizeof( float ) );
    fltInt16    =  ((fltInt32 & 0x7fffffff) >> 13) - (0x38000000 >> 13);
    fltInt16    |= ((fltInt32 & 0x80000000) >> 16);

    return fltInt16;
}

/+ ---- + ---- + ---- + ---- + ---- + ---- + ---- + ---- + ---- + --- -+ ---- + ---- + ---- + ---- + ---- + ---- + ---- + ---- +/

float Float16ToFloat( short fltInt16 )
{
    int fltInt32    =  ((fltInt16 & 0x8000) << 16);
    fltInt32        |= ((fltInt16 & 0x7fff) << 13) + 0x38000000;

    float fRet;
    memcpy( &fRet, &fltInt32, sizeof( float ) );
    return fRet;
 }

/*+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+*/