Member Avatar for iammfa

Hi,
with c++, what is the steps to make centered 2d sprite rotate oriented toward mouse cursor, i heard that i should use trigonometry..
can someone tell me these steps without coding

regards
iammfa

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  • Latest Post Latest Post by mrnutty

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Brief, practical clarifications to complement 's question and the suggestions from and — focused on the common gotchas and a robust math workflow for DarkGDK or any 2D engine.

Common pitfalls: coordinate orientation (many 2D APIs use a top‑left origin so Y grows downward), sprite pivot not actually centered, engine rotation units (degrees vs radians), and wrapping when interpolating across 0/360. For stable results prefer an angle routine that handles quadrants (atan2) and apply an artwork-facing offset if the sprite image’s “forward” isn’t the math zero.

Core math (no full API code):

  • Compute delta from sprite center to mouse (adjust for any non-centered pivot).
  • Use atan2(dy, dx) to get the signed angle in radians (handles quadrants and avoids divide-by-zero).
  • Convert to degrees if the engine expects degrees and subtract the sprite-art offset (common offsets: 0, 90, -90 depending on how the sprite was drawn).
  • Assign that angle to the sprite rotation.

Example pseudocode:

dx = mouseX - spriteCenterX
dy = mouseY - spriteCenterY   # invert sign if screen Y grows downward for the math convention used
angleRad = atan2(dy, dx)
angleDeg = angleRad * 180.0 / PI
angleDeg -= artworkFacingOffset
sprite.rotation = angleDeg

Troubleshooting and polish: set the sprite pivot to its center (or include the offset in the center calculation); normalize angle differences to the shortest path (map to [-180,180]) before lerping to avoid long rotations; multiply rotation velocity by frame delta for frame-rate independence; draw a debug line from center to mouse and print the computed angle when the result looks wrong. For many sprites, avoid excessive trig calls per frame by updating only when the mouse moves or at a coarse interval.

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Member Avatar for mrnutty

How are you getting the sprite to be displayed, meaning what graphics library are you using?

Edited by mrnutty because: n/a
Member Avatar for iammfa

in fact, I'm using DarkGDK, only i hope guide lines not code

Member Avatar for mrnutty

First you need to get the mouse's position. Then you need to know the
position vector of the sprite. Then you need to rotate the sprite
until its axis aligned with the where the mouse is. You can use the
sin function to orient the position vector of the sprite in a way that its
axis aligned with the mouses position.

If you don't know what axis aligned means then take a look

As you can see you will also have to calculate the line from x = 0
to x = MAX where the line needs to intersect the sprite position.
Then you will have to do the same for the mouse point. And lastly
you need to rotate the mouse until its line is very similar to that of the
mouse's point.

Member Avatar for mikiurban

Another way is to determine the angle of a line from the center of the screen to your mouse, then rotate your image that much. Don't forget to check the mouse position constantly, either using a timer (like every x seconds) or every time the mouse moves.

Member Avatar for mrnutty

Actually you can also use Pythagorean. Make a right trials with the end point from the center of the sprite and the mouse clicked point, then
all you have to do is rotate the sprite by using the sin function until the
y component of the right triangle goes to 0.

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