Return to Revisions

I'm assuming you are generating a scaling matrix to perform zoom.

First is the easy part(you probably have this already). You want is to stop zooming when the background becomes the same size as the viewport. The point to stop zooming out is 'backgroundwidth/viewportwidth'. This will be 0.5 in your case. Don't let the zoom factor go below this value.

This will work fine if the camera is in the centre of the background, but if the camera is off centre, you will still see your cornflower blue on the edge of the screen.

In order to prevent the user from being shown outside the edge of the world, yo will need to change the size of playerBounds rectangle. You are already using this to stop camera movement when the player gets too close to the edge. You just need to make sure that this rectangle has the appropriate size. Basically you want to prevent the camera position from getting within camerawidth/2 pixels of the edge of the background. During zooming out the background is effectively getting smaller

float scaledWorldHalfWidth=worldSize.x*cam.Zoom/2.0f;
float scaledWorldHalfHeight=worldSize.y*cam.Zoom/2.0f;

playerBounds = new Rectangle(worldcentre.X-scaledWorldHalfWidth +CameraViewport.X/2,
                             worldcentre.Y-scaledWorldHalfHeight+CameraViewport.Y/2,
                             worldcentre.X+scaledWorldHalfWidth -CameraViewport.X/2,
                             worldcentre.Y+scaledWorldHalfHeight -CameraViewport.Y/2);

In this code I am decreasing the size of the rectangle as the zoom factor decreases (as the player sees more and more of the background).

EDIT

This new player bounds should be generated whenever you change the camera zoom factor. So call it when 'q' or 'a' is pressed.

Also, whenever the camera moves check if the camera is still in playerbounds, if not adjust it position so that it is;

        if (cam._Pos.X < playerBounds.Left) //too far left? Any further left, the camera will start to show the edge of the map
            cam._Pos.X=playerBounds.Left //put it on the left most edge player bounds
                                         
         // similar code needed for top, bottom and right

A couple of other things;

1. As you zoom out, you will need to check if camera position still lies within the playerBounds rectangle, as the rectangle gets smaller. You will need to adjust/move the camera to make sure it lies in the rectangle.

2. All this code will be implemented much simpler if you centre the world on the origin, rather than having the upper-left of the world drawn at the origin. (check out the 'origin' parameter in spritebatch.Draw(.....);