SDL: Bug: SDL_SetRelativeMouseMode() does not restore cursor position correctly

https://github.com/libsdl-org/SDL/assets/77922942/8d228139-6b8d-462b-9330-9ee159ec1a0f

Using Love2D 11.4 on Windows, tested both the default distribution as well as with SDL.dll replaced to latest release.

crosshairX, crosshairY = 0 , 0
posX, posY = 0 , 0
panning = false
function love.mousepressed( x, y, button, istouch, presses )
    if button==3 then 
       crosshairX , crosshairY = x , y
       panning = true
       love.mouse.setRelativeMode(true)
    end
end
function love.mousereleased( x, y, button, istouch, presses )
    if button==3 then 
       love.mouse.setRelativeMode(false)
       panning = false
       crosshairX , crosshairY = 0 , 0
    end
end
function love.mousemoved( x, y, dx, dy, istouch )
    if panning then 
       posX = posX + dx
       posY = posY + dy
    end
end
function love.draw()
    local w,h = love.graphics.getDimensions()
    local x,y = w/2 - posX , h/2 - posY
    love.graphics.rectangle('line',x-50,y-50,100,100)
    love.graphics.line(x,0,x,h)
    love.graphics.line(0,y,w,y)
    if panning then
       love.graphics.line(crosshairX,0,crosshairX,h)
       love.graphics.line(0,crosshairY,w,crosshairY)
    end
end

About this issue

Original URL
State: open
Created a year ago
Comments: 22 (14 by maintainers)

Most upvoted comments

Ah I see, it’s a bit ambiguous here whether we’re talking about the OS logical cursor position or SDL’s internal position when we say “mouse position”. Indeed this will solve the usecase.

Perhaps can we also have a flag that keeps the cursor visible at where it’s logically locked to (screen center), for those who really want the under-the-hood behavior to be visible?

Or maybe just make it a different API call altogether that has the more fine-grained control over what you want, rather than overloading the out-of-box experience of the RelativeMode API with flags? Something that lets you declare that you want to subscribe to a particular input source, rather than setting a global state. This architecture would also open the door for easier ManyMouse integration. These are just spurious suggestions so take it with a grain of salt, the main point is to conveying the existence of a desired usecase.

SDL has code internally to replicate the OS mouse acceleration curves, so for applications that do want normal mouse motion while also getting relative deltas (e.g. scrolling the map at the edge of the window), it is much easier for an application to draw a cursor at a fixed location than to try to replicate the mouse acceleration algorithm.

Out of curiosity, could you elaborate a bit more on what you meant with the map edge scrolling mechanic?

expikr on Jun 29, 2023