Texture.cpp

#include "Texture.hpp"

#include "stb_image/stb_image_include.h"

ImageTexture::ImageTexture(const char * filename)
{
    auto components_per_pixel = bytes_per_pixel;

    data_ = stbi_load(filename, &width_, &height_, &components_per_pixel, components_per_pixel);

    if (!data_) {
        std::cerr << "ERROR: Could not load texture image file '" << filename << "'.\n";
        width_ = height_ = 0;
    }

    bytes_per_scanline_ = bytes_per_pixel * width_;
}

Color ImageTexture::value(Real u, Real v, const Vector3 & p) const
{
    // If we have no texture data, then return solid cyan as a debugging aid.
    if (data_ == nullptr)
        return Color(0, 1, 1);

    // Clamp input texture coordinates to [0,1] x [1,0]
    u = clamp(u, 0.0, 1.0);
    v = 1.0 - clamp(v, 0.0, 1.0);  // Flip V to image coordinates

    auto i = static_cast<int>(u * width_);
    auto j = static_cast<int>(v * height_);

    // Clamp integer mapping, since actual coordinates should be less than 1.0
    if (i >= width_)  i = width_ - 1;
    if (j >= height_) j = height_ - 1;

    const auto color_scale = 1.0 / 255.0;
    auto pixel = data_ + j * bytes_per_scanline_ + i * bytes_per_pixel;

    return Color(color_scale*pixel[0], color_scale*pixel[1], color_scale*pixel[2]);
}