Jump to content
  • Advertisement
Sign in to follow this  

How do I use my scroll bar to increment a std::vector

This topic is 2042 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hello all.


Ok I have my list box its a std::vector.

My scroll bar moves within the ranges of -104 to - 230


my question is how do I use the scroll ranges to move my list elements

my list elements start at 0 to max entrys.


I think its more complicated because the number of entrys you can see at a time is 4 so I can scroll the bar down 4 slots before it needs to move

any elements into view.

What would you all do.This is my first ever scroll bar I normally go for the arrow keys.

Share this post

Link to post
Share on other sites

You need to convert your scrollbar position into an index into the vector so you know the first item to draw. Then its easy, you draw the next three items after that one.


So -104 to 230, that's a total range of 334. So your scrollbar range is between 0 and 334 if you normalize it into positive coordinates. Now say you have ten items in your list. You display 4 at a time, so your scrollbar needs to be able to have the first index as 0 - 6 (10 - 4) so that in its bottom position, it is showing the last 4 items.


So 334 / 6 = 55.667. So divide your scrollbar position by 55.667 and truncate it to int to get a number between 0 and 6. That is the index of the vector that is the first one that should be drawn.


Sort of. It depends if you want smooth scrolling or not but that's the idea.

Share this post

Link to post
Share on other sites

Thanks All. It works well

init code

//we need to calculate the delta range this range is maped to the total amount in the list box
	ScrollDelta = fabs(ScrollRangeMin - ScrollRangeMax);

	//the ScrollIncrement is the amount we can move for each slot of the list box
	//its the number of list Items devided by the ScrollDelta
	//this maps the range of the slider to the number of items in the list box
	ScrollIncrement = ScrollDelta / (NumberDlgs - MaxDisplayListItems);

	//set the default range and check to see if the number of dlg boxes is less then max display items
	VectorEndRange = MaxDisplayListItems;
	if(NumberDlgs < MaxDisplayListItems)
		VectorEndRange = NumberDlgs;

OnMouse move code

//calculate the display start range
					StartListDisplayElement = fabs(fabs(ScrollRangeMin - v.y) / ScrollIncrement);
					if(StartListDisplayElement < 0)
							StartListDisplayElement = 0;

					if(StartListDisplayElement > ListDialogBox.size() - MaxDisplayListItems)
							StartListDisplayElement = ListDialogBox.size() - MaxDisplayListItems;

					//set the rendering of the list box vector here
					VectorEndRange = StartListDisplayElement + MaxDisplayListItems;

					if(VectorEndRange > ListDialogBox.size())
						VectorEndRange = ListDialogBox.size() - MaxDisplayListItems;

					if(VectorEndRange < 0)
						VectorEndRange = 0;

Render code
for(UINT ctr = StartListDisplayElement; ctr < VectorEndRange; ctr++)
    render items

Here it is


Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Advertisement

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

GameDev.net is your game development community. Create an account for your GameDev Portfolio and participate in the largest developer community in the games industry.

Sign me up!