CODEWITHSUNDEEP
c++openglmouse-coordinates
mr5
mr5

Reputation: 3590

Windows mouse coordinates VS OpenGL mouse coordinates

How can I determine(this isn't the right term to use I know) that, for every position of mouse in a window space, it gets converted to OGL space(-1, 1). In this case, the user moves the mouse very fast, that I assume all of its previous positions are converted into OGL coordinates. What I am trying to say is that...is a common CPU fast enough to do that (to track all previous events) even if my C++ OGL coordinates converter is very computational expensive? lets say I put very time consuming loops in there? or.. very fast method(). How can I assure that no OGL coordinates are skipped out if I move the mouse fast enough? I'm not jumping to any conclusion here or assuming something else might you think.

Edit:

My program main loop is like this(pseudocode):

void Pollevents()
{
    for everyt_obj in this
    {
        if Not Collide()
        {

            Move(x, y) //

        }
    }
}

void MousePos()
{
    mouse.pos = To_OGL_Coord2f()
}

These are separate threads to be executed (But not actually a real thread) Suppose mouse.pos = (0, 0) then I moved the mouse fast enough to make the new mouse.pos to (10, 10). In a single execution of a loop, the mouse position changed very far from where it was before. Now, how can I tell to my program, by implementing Bresenham's line algorithm as mentioned by Christian Rau, that those values generated by that algorithm(not being tracked) have been crossed by the mouse. Will I add another loop for that to step for all those positions?

Upvotes: 1

Views: 956

Answers (1)

Christian Rau
Christian Rau

Reputation: 45968

How can I assure that no OGL coordinates are skipped out if I move the mouse fast enough?

That's not possible, since there is no way to let the OS generate mouse events for each and every point a mouse move would have crossed when tracked with theoretically infinite precision.

The only way to ensure this is to fill the missing points between the two (possibly far away) mouse positions yourself. If you just want to draw a point for each position the mosue moved over (maybe using OpenGL), draw a line instead.

If you on the other hand need those intermediary mouse positions yourself for further computations, you won't get around computing them yourself using some common line rasterization algorithm (like the Bresenham Algorithm, the school book algorithm for line rasterization). What this basically does is compute each point on a discrete grid that a line from one point to another would have crossed (similar to what your graphics card does when converting a line into discrete pixels), so this will generate each discrete mouse position your virtual mouse path has crossed (ignoring any non-linear mouse movement between measurement points).

EDIT: If you don't need a discrete line with proper equal-width characteristics a much easier way than messing with line rasterization would also be to just work with floating point positions and do a simple linear interpolation of the end points, like datenwolf writes in his comment. This will also give you a better timing precision than discrete mouse positions. But it all depends on what you actually want to do with those mouse positions (and now would be a good way to tell us).

EDIT: From your updated question it looks like you need the mouse positions at a high granularity in order to compute the collision of the mouse with some objects. In this case you don't actually need the intermediary points at all. Just take the line from the current mouse position to the previous one (represented as just a pair of points, or whatever theoretical line representation) and compute the collision of the objects with that line instead of the individual points.

Upvotes: 4

Related Questions