Map scrolling and SetOrigin

BlitzMax Forums/BlitzMax Beginners Area/Map scrolling and SetOrigin

blackwater (Posted 2011) [#1]

Hi everyone, I really burned a few brain cells on this one but I just don't get it! My game screen is 1024x768 with SetOrigin set 0,0 I have a single object at let's say x 300 and y 300 I wrote a tiny bit of code that when the mouse is on the edges of the screen it scrolls the map. So, when I have the mouse on the left hand side, I use the SetOrigin command to subtract a set number from x, so one scroll, X is now at -20 and then the screen gets redrawn. The actual object coordinates aren't changed. Here is what I don't understand, the object is moving left instead of right! If the x origin is -20, shouldn't the object position move to the right by 20 pixels? If I keep scrolling, the x origin is -300 but yet the object is drawn right up against the left edge of the screen, which I don't understand because shouldn't it be drawn on the right side of the screen instead? The point of this is that I only draw what is visible on the screen, based on Origin coordinates relative to object coordinates. Any anyone shed some light on this for me? Thanks in advance, hopefully I explained it well enough.

Jesse (Posted 2011) [#2]

you need to add 20 so that the the previous origin( 0,0 ) is now at 20,0 and now you can see from -20 to (screeenwidth() -20) Last edited 2011

Floyd (Posted 2011) [#3]

Here's an earlier discussion: SetOrigin debate, complete with my philosophical ramblings.

Czar Flavius (Posted 2011) [#4]

In this post there is a simple game with scrolling. Press enter to start it. http://blitzbasic.com/Community/posts.php?topic=90762#1033024

blackwater (Posted 2011) [#5]

Thanks, after reading that thread I have a better understanding of how SetOrigin works. I was convinced I had to be doing something wrong since it was working "backwards"