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Float to pixel - Width

Started by WinRad Aug 17, 2008 at 4:26 PM 3 replies 1.2k views

Original Post

Aug 17, 2008 at 4:26 PM

Hello again guys, First of all the part one to this question was answered in another thread - "How to convert an object's world coordinates into screen space coordinates?". This question is a bit different though obviously... "How can I figure out the width of a point sprite if I know its size and its center?". So basically I have a point sprite and using the technqiue mentioned in the part 1 of this thread figured out the sprite's center's position on the screen, but I need to create a bounding box around it. So since I know the size which is 0.3f I should be able to work out the bounding box by doing something like -> SpriteCentreLeft = Centre - 0.3f; Or something like that, but I have no idea on what to do! Please help out. Thanks!

Ebola0001

Aug 17, 2008 at 10:43 PM

well if the point sprite is 0.6f wide in world space, just generate a point in the upper left and lower right in world space, then transform those points as discussed in the other thread

WinRad

Aug 18, 2008 at 12:32 PM

Sorry I don't know what you mean, I'm gonna need an example :(. Also I don't remember being tought how to work out an object's size in pixels.

Thanks!

MJP

Aug 18, 2008 at 12:38 PM

Well you said you already worked out how to get the screen-space position from a world-space position, right? Well all you need to do to find out the screen-space width is to convert two world-space points to screen space and calculate the width. So let's assume you have a function that takes world-space and outputs screen-space, called "WorldSpaceToScreenSpace":

spriteCenterSS = WorldSpaceToScreenSpace(spriteCenterWS);spriteRightEdgeSS = WorldSpaceToScreenSpace(spriteCenterWS + 0.3f);spriteWidthSS = spriteRightEdgeSS.x - spriteCenterSS.x;

WinRad

Aug 18, 2008 at 5:23 PM

Wow I feel so stupid... I already tried something similar but it didn't work, but I really thought it should have worked --->

WorldCentreSS = WorldSpaceToScreenSpace(WorldCentreWS);
WorldCentrePlusWidthSS = WorldSpaceToScreenSpace(WorldCentrePlusWidthWS);
WidthSS = WorldCentrePlusWidthSS - WorldCentreSS;

OPTIONAL: What's wrong with that?

RESOLVED.

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