His "magic trick" is twofold.
1. The sprite is at the same resolution as the size of the region it covers at a specific resolution. Ie, a 256x256 sprite covers a 256x256 pixel region, regardless of the screen resoltion. In other words, at higher resoltions, your HUD objects will be smaller.
2. He offsets the object by half a pixel towards the top left of the screen. The reason for this has to do with how bilinear filtering works. Unless you offset by half a pixel, then each pixel is actually displaying a point in the center of 4 pixels. So every pixel's getting averaged with the 4 colors that surround it. The result is that if you took a texture which is vertical or horizontal white and black lines, then unless you offset it like this, what you will actually see on the screen is a solid 50% gray square.
Of course there's one little problem with doing this, I think and that is that there may be a one pixel wide border outside your 640x480 region on the right and bottom of the screen. Though I have not actually tested this to see if that is what you get or not. I do know what if you offset towards the bottom right instea dof towards the upper left you get a border on the top and left sides of the screen.
1. The sprite is at the same resolution as the size of the region it covers at a specific resolution. Ie, a 256x256 sprite covers a 256x256 pixel region, regardless of the screen resoltion. In other words, at higher resoltions, your HUD objects will be smaller.
2. He offsets the object by half a pixel towards the top left of the screen. The reason for this has to do with how bilinear filtering works. Unless you offset by half a pixel, then each pixel is actually displaying a point in the center of 4 pixels. So every pixel's getting averaged with the 4 colors that surround it. The result is that if you took a texture which is vertical or horizontal white and black lines, then unless you offset it like this, what you will actually see on the screen is a solid 50% gray square.
Of course there's one little problem with doing this, I think and that is that there may be a one pixel wide border outside your 640x480 region on the right and bottom of the screen. Though I have not actually tested this to see if that is what you get or not. I do know what if you offset towards the bottom right instea dof towards the upper left you get a border on the top and left sides of the screen.