Texture.cpp

#include "Texture.h"

#include <fstream>
#include <algorithm>

#define FOURCC_DXT1 0x31545844 // Equivalent to "DXT1" in ASCII
#define FOURCC_DXT3 0x33545844 // Equivalent to "DXT3" in ASCII
#define FOURCC_DXT5 0x35545844 // Equivalent to "DXT5" in ASCII

Texture::Texture(char * filePath)
{
    unsigned char header[124];

    FILE *fp;

    fp = fopen(filePath, "rb");
    if (fp == NULL)
        return;

    // check file type
    char filecode[4];
    fread(filecode, 1, 4, fp);
    if (strncmp(filecode, "DDS ", 4) != 0) {
        fclose(fp);
        return;
    }

    //read header
    fread(&header, 124, 1, fp);

    unsigned int height = *(unsigned int*)&(header[8]);
    unsigned int width = *(unsigned int*)&(header[12]);
    unsigned int linearSize = *(unsigned int*)&(header[16]);
    unsigned int mipMapCount = *(unsigned int*)&(header[24]);
    unsigned int fourCC = *(unsigned int*)&(header[80]);

    unsigned char * buffer;
    unsigned int bufsize;

    bufsize = mipMapCount > 1 ? linearSize * 2 : linearSize;
    buffer = new unsigned char[bufsize];
    fread(buffer, 1, bufsize, fp);

    fclose(fp);

    unsigned int components = (fourCC == FOURCC_DXT1) ? 3 : 4;
    unsigned int format;
    switch (fourCC)
    {
    case FOURCC_DXT1:
        format = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
        break;
    case FOURCC_DXT3:
        format = GL_COMPRESSED_RGBA_S3TC_DXT3_EXT;
        break;
    case FOURCC_DXT5:
        format = GL_COMPRESSED_RGBA_S3TC_DXT5_EXT;
        break;
    default:
        delete buffer;
        buffer = nullptr;

        return;
    }


    glGenTextures(1, &m_texture);


    glBindTexture(GL_TEXTURE_2D, m_texture);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);


    unsigned int blockSize = (format == GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) ? 8 : 16;
    unsigned int offset = 0;


    for (unsigned int level = 0; level < mipMapCount && (width || height); ++level)
    {
        unsigned int size = ((width + 3) / 4)*((height + 3) / 4)*blockSize;
        glCompressedTexImage2D(GL_TEXTURE_2D, level, format, width, height,
            0, size, buffer + offset);

        offset += size;
        width = std::max(width / 2, 1u);
        height = std::max(height / 2, 1u);
    }


    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, (mipMapCount == 0) ? 0 : mipMapCount - 1);

    glGenerateMipmap(GL_TEXTURE_2D);

    delete buffer;
    buffer = nullptr;


    const GLfloat g_uv_buffer_data[] =
    {
        0.0f, 1.0f - 0.0f,
        0.5f, 1.0f - 0.5f,
        1.0f, 1.0f - 0.0f
    };

    GLuint uvBuffer;
    glGenBuffers(1, &uvBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, uvBuffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(g_uv_buffer_data), g_uv_buffer_data, GL_STATIC_DRAW);


    glEnableVertexAttribArray(1);
    glBindBuffer(GL_ARRAY_BUFFER, uvBuffer);
    glVertexAttribPointer(
        1,
        2,
        GL_FLOAT,
        GL_FALSE,
        0,
        (void*)0
    );

    glBindTexture(GL_TEXTURE_2D, 0);
}


Texture::~Texture()
{
    glDeleteTextures(1, &m_texture);
}

void Texture::Bind()
{
    glBindTexture(GL_TEXTURE_2D, m_texture);
}