RTVolumeRendering/Source/TransferTexture.cpp

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#include <assert.h>
#include "TransferTexture.h"

//----------------------------------------------------------
TransferTexture::TransferTexture() : tex(0), boundUnit(-1) {}

//----------------------------------------------------------
TransferTexture::~TransferTexture()
{
        if(tex)
                glDeleteTextures(1, &tex);
}

//----------------------------------------------------------
bool TransferTexture::Load(const char *name)
{
        return true;
}

//----------------------------------------------------------
bool TransferTexture::CreateFunction(const std::vector<PlotPoint> &red,
                                                                         const std::vector<PlotPoint> &green,
                                                                         const std::vector<PlotPoint> &blue,
                                                                         const std::vector<PlotPoint> &alpha)
{
        float color[256 * 4]; // holds RGBA data interpolated from the plots
        
        if( !(Interpolate(red,   color    , 4) &&
              Interpolate(green, color + 1, 4) &&
              Interpolate(blue,  color + 2, 4) &&
              Interpolate(alpha, color + 3, 4)) )
        {
                return false;
        }
        
        if(tex)
                glDeleteTextures(1, &tex);
        
        glGenTextures(1, &tex);
        glBindTexture(GL_TEXTURE_1D, tex);
        glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP);
        glTexImage1D(GL_TEXTURE_1D, 0, GL_RGBA, 256, 0, GL_RGBA, GL_FLOAT, (GLvoid*)color);
        glBindTexture(GL_TEXTURE_1D, 0);
        
        return true;
}

//----------------------------------------------------------
bool TransferTexture::Interpolate(const std::vector<PlotPoint> &plot, float *color, int stride)
{
        int count = (int)plot.size();
        
        int min = plot[0].dataValue;
        int max = plot[count - 1].dataValue;
        int len = max - min;
        
        if(max < 255 || min > 0) 
                return false;
        
        int curr = 0;
        int n = (int)(count - 1);
        for(int i = 0; i < n; i++)
        {
                int amt = plot[i + 1].dataValue - plot[i].dataValue;

                float c0 = plot[i].value;
                float dc = plot[i + 1].value - c0;
                
                for(int j = 0; j < amt; j++)
                {
                        float t = (float)j / amt;
                        color[curr] = c0 + dc * t;

                        curr = curr + stride;
                }
        }
        
        color[curr] = plot[count - 1].value;
        
        return true;
}

//----------------------------------------------------------
void TransferTexture::Bind(int unit)
{
        if(unit < 0 || unit > GL_MAX_TEXTURE_UNITS)
                return;
        
        if(boundUnit != -1)
                return; // we are already bound to a texture unit
        
        glActiveTexture(GL_TEXTURE0 + unit);
        glBindTexture(GL_TEXTURE_1D, tex);
        
        boundUnit = unit;
}

//----------------------------------------------------------
void TransferTexture::UnBind()
{
        if(boundUnit != -1)
        {
                glActiveTexture(GL_TEXTURE0 + boundUnit);
                glBindTexture(GL_TEXTURE_1D, 0);
                
                boundUnit = -1;
        }
}

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