Get QVector<unsigned char> with all the data of an image

JesusM

How can I get a QVector<unsigned char> with all the data of a QImage?
I need to get all the unsigned char information of an image to use it as a texture in the GPU.

jsulm

@JesusM Why do you want to have the data in a QVector?! It would be quite inefficient.
There is https://doc.qt.io/qt-5/qimage.html#bits which you should use.
Even better is https://doc.qt.io/qt-5/qimage.html#constBits

JesusM

@jsulm
I need to translate this code to QT. This coe is done un MVS 2017 with c++ and I needed to use an external class to read the image

PagTexture::PagTexture(std::vector<std::string> rutas, std::vector<PagTexturesTypes> tipo)
{
	for (int i = 0; i < rutas.size(); i++)
	{
		std::string filename = rutas[i];
		PagTexturesTypes tipoTextura = tipo[i];
		/** Carga un png de disco https://lodev.org/lodepng/ */
		std::vector<unsigned char> image; // Los píxeles de la imagen
		unsigned width, height;
		unsigned error = lodepng::decode(image, width, height, filename);
		if (error)
		{
			std::cout << filename << " cannot be loaded" << std::endl;
			return;
		}
		// La textura se carga del revés, así que vamos a darle la vuelta
		unsigned char *imgPtr = &image[0];
		int numColorComponents = 4;
		int wInc = width * 4; //width in char
		unsigned char* top = nullptr;
		unsigned char* bot = nullptr;
		unsigned char temp = 0;
		for (int i = 0; i < height / 2; i++)
		{
			top = imgPtr + i * wInc;
			bot = imgPtr + (height - i - 1) * wInc;
			for (int j = 0; j < wInc; j++)
			{
				temp = *top;
				*top = *bot;
				*bot = temp;
				++top;
				++bot;
			}
		}

		//Construimos la textura con las imágenes que queremos y la función de cada imagen
	
				GLuint texture = 0;
				glGenTextures(1, &texture);
				glBindTexture(GL_TEXTURE_2D, texture);
				glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
				glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
				glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
				glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
				glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height,0, GL_RGBA, GL_UNSIGNED_BYTE, image.data());
				glGenerateMipmap(GL_TEXTURE_2D);

				this->color = new PagImagen(image,width,height,texture);
				
               }
}

So I am using QImage but I don't know hoow to translate this lane .

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height,0, GL_RGBA, GL_UNSIGNED_BYTE, image.data());

What I've done by now is this. I used the .bit() you told me:

texture::texture(QVector<QString> rutas, QVector<TexturesTypes> tipo)
{
    for (int i = 0; i < rutas.size(); i++)
    {
        QString filename = rutas[i];
        TexturesTypes tipoTextura = tipo[i];

        QImage* imagen = new QImage(filename); // Los píxeles de la imagen
        int width, height;

        if (imagen == nullptr)
        {
            std::cout << filename.toStdString() << " cannot be loaded" << std::endl;
            return;
        }
        // La textura se carga del revés, así que vamos a darle la vuelta
        QImage imagenInvertida = imagen->rgbSwapped();
        width = imagenInvertida.width();
        height = imagenInvertida.height();
        
        //Construimos la textura con las imágenes que queremos y la función de cada imagen

                GLuint texture = 0;
                glGenTextures(1, &texture);
                glBindTexture(GL_TEXTURE_2D, texture);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
                glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height,0, GL_RGBA, GL_UNSIGNED_BYTE, imagenInvertida.bits());
                //glGenerateMipmap(GL_TEXTURE_2D);

                this->color = new image(&imagenInvertida,width,height,texture);
              }
}

Is that rigth now? Is it tha same as I had before?.

SGaist

Hi,

It might be simpler to use a QOpenGLTexture.

JesusM

@SGaist so, if I use QOpenGLTextures, is it better to use QShaderProgram and QVertexArrayObjects instead of doing all the steps to get a GLuint id with the opengl functions?

SGaist

Depending on what where you would like to go with your application, you should consider studying modern OpenGL and go through the related Qt examples.

JesusM

@SGaist I am doing an OpenGL application to play with light settings in diferrent scenes woth different objects and materials

SGaist

Then I confirm my last suggestion.

JesusM

@SGaist ok, perfect so. Thanks a lot