Hi,

I'm trying to draw an overlay quad/shape on top of another quad.

Now i could have my background quad zoomed in (using ortho camera) while i'm trying to draw my overlay object.

Thus, what i really want is to draw the overlay shape which takes into consideration how much i'v already zoomed in.

As currently it doesn't expand/enlarge when i zoom in and thus keeps the overlay shape of the same size.

Do i need to manually enlarge the shape and then draw or could it be all done in shader ?

Any suggestion how i could approach this.

Note: Using SharpDx & C# & Directx11

A picture of what you're trying to do might help.

But, if I'm picturing this in my head correctly, you could use a Scaling Matrix on the quad, in which the amount of scaling would be correlative to the difference between the last frames zoom value, and the current frames zoom value. (Really anything to use as a scalar for the scaling of the overlay)

Using a scaling matrix is pretty simple to. Something like this:

worldMatrix = scale() * rotation() * translation();

Marcus Hansen

Thanks for the reply @markypooch

I tried to upload some screenshots but for some reason they wont upload (no specific reason)

so i have uploaded them to my dropbox.

Screenshot 1 Link: Scenario where the overlay quad (in yellow) are drawn on background quad

Screenshot 2 Link: Scenario where i have zoomed in and then drawn my overlay (in yellow)

Also,

My quads are drawn using actual screen co-ordinates which are transformed to world space in the shader file.

All the quad i.e both background and overlay use the same matrices.

However, at this point I cant understand how would the scaling matrix fit as a solution ?

Would you kindly explain/elaborate.

Thanks

Well now that I see what you're trying to do. Than, yeah a scaling matrix isn't much of a solution. I was kinda going off this:

Thus, what i really want is to draw the overlay shape which takes into consideration how much i'v already zoomed in

As currently it doesn't expand/enlarge when i zoom in and thus keeps the overlay shape of the same size.

A scaling matrix will scale the quad by some magnitude of your choosing. This is, it can enlarge the quad itself the more you zoom up on the license plate. But, it all depends on what you're trying to do.

If your expecting an algorithm to run through all sorts of different pictures of cars with license plates, and occlude them, you may want to look into an image detection algorithm, which if that's the case, i'll pass this topic off to someone else who has more knowledge in this area.

Marcus Hansen

The way i zoom is i try to keep the point under the mouse at the same position by moving quad left/right/top/bottom if it needs to.

Also, i wasn't expecting an image detection algorithm. The background image used was from live camera feed.

Why not just render the image background image to an offscreen texture, add the yellow boxes, and then use this new image to zoom in on?

thanks for the update @Norman Barrows

Yes i agree as after researching & reading on it.

However from what i read rendering to texture can have performance issues.

If this is the case then whats the main reason/best case scenario for its usage ?

Also the confusion i still have :

1. As to how to copy it over to back buffer as in my case Invalidate the surface as using D3DImage (part of WPF) ?

2. How would my ortho camera work in this case.

Though i'm still investigating the above two points, since i've just started to implement it in code.