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I'm drawing a health bar on top of each player. I transform 3d position to 2d. I would like to draw it smaller when distance increases. Any simple math for that? Let's say bar width is 30 and height is 10 it looks good only on distance == 100. What formula should I use to make it decrease in size when distance increases?

Should resolution of the game be taken into consideration?

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  • \$\begingroup\$ This sounds a lot like actual 3D rendering, so any papers/tutorials on it could be useful for you. \$\endgroup\$ – ZEKE Oct 30 '17 at 19:55
  • \$\begingroup\$ @ZEKE it's about math here, width, height and scale based on distance. Rendering is done in 2D. \$\endgroup\$ – Konrad Oct 30 '17 at 20:01
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The very complex and hard to understand calculation people do to get an object's size at a specific distance is: divide by Z. Even the big APIs, like DirectX and OpenGL are basically just rasterizing APIs with a depth buffer. The 3d aspect comes from this. So:

Given a width, a height and a distance from the camera Z, the new width and height of the object is:

w' = w / Z
h' = h / Z
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    \$\begingroup\$ One detail, if you find it looks right at its base scale at referenceDistance = 100 then throw that in as a multiplicative factor: w' = w * referenceDistance / distance - that way the multiplier comes out to 1 at the reference distance you've chosen, and scales appropriately closer & farther away. \$\endgroup\$ – DMGregory Oct 31 '17 at 3:57

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