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Graphics / Text transformations and OpenGL

« on: October 11, 2013, 05:21:10 pm »

Hello,

I want to do some transformations (rotations around all three axes) to some text and display it with SFML. I don't see a good way to do this. The problem is that the RenderWindow::draw() method appears to clear the modelview matrix.

I have some code here which works if I change Transform::m_matrix to public.

It would be nice to be able to set all of the transform's matrix. Is there a way to do this without hacking the library?

Code: [Select]

#include <SFML/Window.hpp>
#include <SFML/Graphics.hpp>
#include <SFML/OpenGL.hpp>
#include <time.h>

int main()
{
    // create the window
    sf::RenderWindow window(sf::VideoMode(800, 600), "OpenGL", sf::Style::Default, sf::ContextSettings(32));
    window.setVerticalSyncEnabled(true);

    // load resources, initialize the OpenGL states, ...
    sf::Font font;
    if (!font.loadFromFile("c:/windows/fonts/Arial.ttf"))
    {
        // error...
    }

    sf::Text text;

    // create a transform
    sf::Transform t;

    // select the font
    text.setFont(font); // font is a sf::Font

    // set the string to display
    text.setString("Hello world");

    // set the character size
    text.setCharacterSize(24); // in pixels, not points!
 
    // set the color
    text.setColor(sf::Color::Red);

    // set the text style
    text.setStyle(sf::Text::Bold | sf::Text::Underlined);


    // run the main loop
    bool running = true;
    while (running)
    {
        // handle events
        sf::Event event;
        while (window.pollEvent(event))
        {
            if (event.type == sf::Event::Closed)
            {
                // end the program
                running = false;
            }
            else if (event.type == sf::Event::Resized)
            {
                // adjust the viewport when the window is resized
                glViewport(0, 0, event.size.width, event.size.height);
            }
        }

        // clear the buffers
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // draw using SFML... rotate the text starting 1080 ms after program launch
        t=sf::Transform::Identity;
        t.translate(200,300);
        if (clock()>1080)
        {
           t.rotate((float)(clock()%360));
        }

        // apply the transform to the text
        window.draw(text,t);

        // do our own rotation
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        glTranslatef(500.0, 300.0, 100.0);
        if (clock()>1080)
           glRotatef((float)(clock()%360),0.0,0.0,1.0); // around z axis

        // save the matrix
        float matrix[16];
        glGetFloatv(GL_MODELVIEW_MATRIX, matrix);

        // set the transform's matrix equal to the saved modelview matrix
        // (i had to make m_matrix public to do this :(
        for (int i=0; i<16; i++)
           t.m_matrix[i]=matrix[i];

        window.draw(text,t);

        // end the current frame (internally swaps the front and back buffers)
        window.display();
    }

    // release resources...

    return 0;
}