SOIL - Getting Image Dimensions

Question

I have decided to use SOIL to load images for use with OpenGL for my project. I have this method, which loads an image and returns a GLTexture, which is a struct that hold a GLuint textureid and two ints width and height:

GLTexture loadTexture(const char *filePath) {
GLTexture texture = {};
int width;
int height;
unsigned char *data;

//Load Image File Directly into an OpenGL Texture
texture.id = SOIL_load_OGL_texture
    (
    filePath,
    SOIL_LOAD_AUTO,
    SOIL_CREATE_NEW_ID,
    SOIL_FLAG_MIPMAPS | SOIL_FLAG_INVERT_Y | SOIL_FLAG_NTSC_SAFE_RGB | SOIL_FLAG_COMPRESS_TO_DXT
    );

//Error Checking (Load Process)
if (texture.id == 0) {
    fatalError("SOIL Loading Error!");
}

//Generate and Bind Texture
glGenTextures(1, &(texture.id));
glBindTexture(GL_TEXTURE_2D, texture.id);

//Get Width, Height and Data of Image
glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, &width);
glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT, &height);
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, &data);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, &data);
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);
glGenerateMipmap(GL_TEXTURE_2D);

//Unbind Texture
glBindTexture(GL_TEXTURE_2D, 0);

//Return Texture
texture.width = width;
texture.height = height;
return texture;

}

As far as I know, glGetTexLevelParameteriv() should return the width of the texture that is binded into width and height, but whenever I load an image, this returns 0.

Should I fill in width and height as parameters for the method or is it possible to get them via OpenGL?

Answer 1

The texture id generated by SOIL_load_OGL_texture is overridden in the

glGenTextures(1, &(texture.id));

line (glGenTextures creates a new texture and stores the id in &(texture.id)). All operations afterwards work on the newly created texture. Since this new texture is empty, width and height are 0.

I'm not sure what you want to achieve here, but if you only want to load the texture, then this code might work:

texture.id = SOIL_load_OGL_texture    (...);

//Error Checking (Load Process)
if (texture.id == 0) {
    fatalError("SOIL Loading Error!");
}

//Just bind and do not create a new texture
glBindTexture(GL_TEXTURE_2D, texture.id);

glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, &width);
glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT, &height);

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);
glGenerateMipmap(GL_TEXTURE_2D);

//Unbind Texture
glBindTexture(GL_TEXTURE_2D, 0);

//Return Texture
texture.width = width;
texture.height = height;
return texture;