Tilemap rendering issues

[MrShedman]

Can anyone explain why I get these rendering quirks on different GPU's?

AMD HD5850: Looks perfect no artifacts


nVidia Gefore GT 740M: Some tiles shift upwards/downards by 1 pixel but leave no gaps


Intel 4400:  Only horizontal gaps and weird shifting inside the tiles

[Nexus]

I guess you're using non-integral coordinates. Different graphics cards may rasterize the texture in different ways. If you need pixel-perfect rendering, round everything (see the note in the documentation of Drawable.hpp I recently added).

There are many threads about this and some related issues on the forum, e.g. this one, this one or this one.

[MrShedman]

Each tile in my tileset texture is 48x48 and the same on screen, so the 1:1 mapping shouldn't be the problem.

The tilemap is never moved, only the view is moved and each tile on startup is given and integer position and size (although casted to a float to work with sf::Vertex)

The code below is what I'm using to draw the tilemap.

void draw()
{
        sf::View view = window->getView();
        float cx = view.getCenter().x;
        float cy = view.getCenter().y;
        float x = cx - window->getSize().x / 2;
        float y = cy - window->getSize().y / 2;
        cx = std::floor(cx);
        cy = std::floor(cy);

        view.setCenter(cx, cy);
        rTexture.setView(view);

        rTexture.clear(sf::Color::Transparent);
        rTexture.draw(*map);
        rTexture.display();

        const sf::Texture& texture = rTexture.getTexture();

        // draw it to the window
        sf::Sprite sprite(texture);
        sprite.setPosition(x ,y);

        window->draw(sprite);
}
 

[ncsu121978]

moving the view or moving the tilemap is essentially the same thing anyway ultimately to the video card doing the actual rendering.  It is ultimately trying to render your tiles at a non-integer location and with floating point precision not being perfect can lead exactly to the problem you are seeing.

I would suggest to keep a floating point location for your view, but before rendering, round/cast it to the closest integer.

[MrShedman]

After hours of googling and several dodgy hacks later I came upon one method that works 100% on all of my different set-ups!

float x = view.getCenter().x;
float y = view.getCenter().y;

x = std::floor(x);
y = std::floor(y);
x += 0.375f;
y += 0.375f;

view.setCenter(x, y);

I was already rounding the views co-ords to integers, but adding 0.375f draws the tiles pixel-perfect every time!

[Nexus]

Strange... I remember that this 0.375 offset was once included in SFML because of exactly this problem. And for me personally, pixel-perfect rendering always worked with simple rounding of coordinates -- as long as I really did it for all the involved ones.

Are you using an outdated SFML version?

[MrShedman]

It does seem strange although I found this "hack" in several forums and the general reasoning behind it was AMD/nVidia round floating point numbers differently.

I'm using whatever was the latest revision on github about a month ago, so as far as I can see from the commits nothing has been changed that would affect this.