C++ OpenGL Texture not loading

Question

void OGLRectangle::LoadTexture(const char* filename)
{
unsigned int texture;
int width, height;
BYTE * data;
FILE * file;

file = fopen(filename, "rb");

width = 1920;
height = 1080;
data = new BYTE[height * width * 3];

fread(data, width * height * 3, 1, file);
fclose(file);

glGenTextures(1.0, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
tex = texture;
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

glTexImage2D(GL_TEXTURE_2D, 0, 2, width, height,0, GL_RGB, GL_UNSIGNED_BYTE, data);

delete [] data;

}

I have this code to render in an image, the method is called with: LoadTexture("C:\\Users\Rhys\Documents\Hills.bmp"); The file exists.

Then I'm trying to render it to the openGL window using;

    glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, tex);
glBegin(GL_QUADS);
glTexCoord2d(0.0, 0.0); glVertex2d(0.0, 0.0);
glTexCoord2d(1.0, 0.0); glVertex2d(100.0, 0.0);
glTexCoord2d(1.0, 1.0); glVertex2d(100.0, 100.0);
glTexCoord2d(0.0, 1.0); glVertex2d(0.0, 100.0);
glEnd();
glDisable(GL_TEXTURE_2D);

However, all I'm getting on screen is a darkish blue box, with no texture rendered in it. I have searched for tutorials on how to do this, even asked my lecturer and I still cannot seem to find out why its not working. Any help will be greatly appreciated.

The BMP file format isn't quite that simplistic. (It's odd that your lecturer is unaware of this.) — molbdnilo
– molbdnilo, Commented Nov 11, 2015 at 15:06

Mykola · Accepted Answer · 2015-11-27 14:10:09Z

The .bmp files loading must be little different

This code simply loads bmp file to memory m_pcbData without compression and indexed color support.

bool CBMPImage::LoadFromFile(const CString& FileName)
{
    BITMAPINFOHEADER BitmapInfo;
    ZeroMemory(&BitmapInfo, sizeof(BITMAPINFOHEADER));

    BITMAPFILEHEADER BitmapFile;
    ZeroMemory(&BitmapFile, sizeof(BITMAPFILEHEADER));

    std::ifstream FileStream(FileName, std::ios::binary | std::ios::in);

    if (!FileStream.good())
        return false;

    // Read bitmap file info
    FileStream.read(reinterpret_cast<char*>(&BitmapFile), sizeof(BITMAPFILEHEADER));
    // Read bitmap info
    FileStream.read(reinterpret_cast<char*>(&BitmapInfo), sizeof(BITMAPINFOHEADER));

    // Proper bitmap file supports only 1 plane
    if (BitmapInfo.biPlanes != 1)
        return false;

    m_cbAlphaBits = 0;
    m_cbRedBits = 0;
    m_cbGreenBits = 0;
    m_cbBlueBits = 0;

    // Retrives bits per pixel info
    m_cbBitsPerPel = (BMPbyte)BitmapInfo.biBitCount;

    // Width and height of image
    m_nWidth = BitmapInfo.biWidth;
    m_nHeight = BitmapInfo.biHeight;

    // Compute bitmap file size
    m_nSize = 4 * ((m_nWidth * m_cbBitsPerPel + 31) / 32) * m_nHeight;

    // Less important info
    m_nPixelWidthPerMeter = BitmapInfo.biXPelsPerMeter;
    m_nPixelHeightPerMeter = BitmapInfo.biYPelsPerMeter;

    // Indexes info not important in our case
    m_nClrCount = BitmapInfo.biClrUsed;
    m_nClrImportant = BitmapInfo.biClrImportant;

    // COMPRESSION MUST BE BI_RGB
    m_Compression = (BMPCompression)BitmapInfo.biCompression;

    delete [] m_pcbData;
    m_pcbData = NULL;

    // Allocate proper data size 
    m_pcbData = new BMPbyte[m_nSize];

    // Read actual image data, considering offset of file header
    FileStream.seekg(BitmapFile.bfOffBits);
    FileStream.read(reinterpret_cast<char*>(m_pcbData), m_nSize);

    FileStream.close();

    return true;
}

than load bmp texture data to OpenGL

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, Image.GetWidth(), Image.GetHeight(), 0, GL_BGR_EXT, GL_UNSIGNED_BYTE, (GLvoid*)Image.GetImageData());

GL_BGR_EXT is important because bmp stores image data in reverse byte order.

Secondly you must specify your material color as white because of usage that texture environment GL_TEXTURE_ENV_MODE, GL_MODULATE

And as mentioned @Reto Koradi, you must specify to generate mipmaps before texture image loading using one of these function calls.

glGenerateMipmap(GL_TEXTURE_2D);

or

glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);

Plus as you used not power of two textures (width = 1920; height = 1080;) it may not work.

Reto Koradi · Accepted Answer · 2016-01-31 03:26:53Z

1

You're setting the attribute to sample with mipmaps:

glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);

You should only set that if your textures actually has mipmaps. To generate mipmaps, you can call:

glGenerateMipmap(GL_TEXTURE_2D);

after the glTexImage2D() call. Or you can simply set the sampler attribute to not use mipmaps:

glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

As has already been pointed out: If your image file is indeed a BMP, and not just a raw image file, your image loading code will also need work.

edited Jan 31, 2016 at 3:26

answered Nov 11, 2015 at 15:17

Reto Koradi

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1 Comment

Mykola Over a year ago

In that case OP must simply get white box consider he uses GL_TEXTURE_ENV_MODE, GL_MODULATE. Because if the box is actualy black, it will be black in all cases.

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