Scene graphs, transformable and transform...

[Wibbs]

Hey,

I'm attempting to implement a simple scene graph, but am having trouble with the way transformable and transform have been implemented and are used by the various drawables.

When traversing the graph to draw each node, you need to be able to apply a cumulative transform to each node. 

However, I cannot see any way of applying this to the node currently being drawn, as the only way of directly changing the orientation of a Drawable is through its Position, Scale and Rotation.  As acumulative transform would be represented as a Transform object, there is no easy way of getting this individual information to use.

Am I missing something obvious here, as I would have thought this should be relatively easy to implement?

Thanks in advance,

Wibbs

[Laurent]

However, I cannot see any way of applying this to the node currently being drawn, as the only way of directly changing the orientation of a Drawable is through its Position, Scale and Rotation.

Transformables have their own transform, but it can be combined with a transform this way:

window.draw(drawable, transform);

[Wibbs]

Ah, thanks - I passed over RenderStates without looking at it in detail because of its name.  Looks like it will do exactly what I need 

[amireldor]

Hello, is there a way to apply a render state to ALL `draw` calls?

I'm trying to scale the whole scene (sprite position and textures) to the window size. i.e. I have a 320x240 background texture and I draw a sprite at 100x100, and then I want to scale the whole scene to fit a 800x600 window.

Currently I have a RenderState with a scale transformation and I pass it to each draw call. It seems funny to do it this way though.

[Nexus]

I'm trying to scale the whole scene (sprite position and textures) to the window size. i.e. I have a 320x240 background texture and I draw a sprite at 100x100, and then I want to scale the whole scene to fit a 800x600 window.

Why don't you just use views?

[amireldor]

I thought about that, but a view only has zoom, and I need scale (I can't zoom differently for X and Y from what I read in the docs).

[Laurent]

zoom() is a convenience function, it's just a hidden call to setSize() that does uniform and relative scaling.

So, to apply a scale factor of (sx, sy) you just have to do this:

view.setSize(view.getSize().x * sx, view.getSize().y * sy);

[Nexus]

As far as I understand your description, you don't want to scale (relatively), rather set the size (absolutely). In your case, to 320x240.

[amireldor]

Alright, thanks for the help! Views it is.

I ended up using:

sf::View view;
view.reset(sf::FloatRect(0, 0, 320, 240));
view.setSize(320, 240);
window.setView(view);

Or more generally:

sf::View view;
view.reset(sf::FloatRect(0, 0, map_width, map_height));
view.setSize(map_width, map_height);
window.setView(view);
 

As I draw my sprites relative to 0, 0 and the edge of the scene is 320, 240.

If I understand correctly, I first reset the View to 'focus' on the (0, 0, 320, 240) of the whole scene, and then I set its size to 320x240 so it shows the whole (0, 0, 320, 240) rectangle (from the 'focus') on the View's viewport which is (0, 0, 1, 1) i.e. the whole screen. Thus I get the (0, 0, 320, 240) to the whole viewport. And all is scaled as I wanted.

[Laurent]

The call to setSize is redundant, the size is already given by the rectangle passed to reset.

[amireldor]

Hmm, yes Laurent, you're right I missed that. I'm posting the final code for the quick copy-paste coders that might bump into this thread.

sf::View view;
view.reset(sf::FloatRect(0, 0, map_width, map_height));
window.setView(view);

[Laurent]

Or

window.setView(sf::View(sf::FloatRect(0, 0, map_width, map_height)));