From: "Graeme Geldenhuys" To: "FPC-Pascal users discussions" Sent: Thursday, October 08, 2009 1:31 AM Subject: [fpc-pascal] X, Y co-ordinate system under OS/2 > Hi, > > I'm porting an OS/2 application to Linux & Windows. From what I can > see in the code, it looks like co-ordinates (0,0) is in the bottom > left corner of the screen. Whereas Windows and Linux, co-ordinates > (0,0) is in the Top Left of the screen. > > Is my assumption correct? If so, DAMN! This is going to cause a lot > of work. :-/ > > > Regards, > - Graeme - Hi Graeme, I know this is a oldish post, but I had some thoughts on this just today :) I'm making a simple GUI system for a game, and I needed to have screen origin independant input coordinates for the GUI (simpler to think about when using), and can be used in different world coordinate systems. So, I have this in my GUI class: properties ---------- FOriginX : Integer; // is the screen's top-left coordinate in final 'world' coordiantes FOriginY : Integer; FDownDir : Integer; // is either +1, or -1 (+1 for world y coordinates increasing downwards, and -1 for increasing upwards methods --------- Function TIMGUI.ScreenToWorldX(Const sx : Integer) : Integer; Begin Result := FOriginX + sx; End; {..............................................................................} {..............................................................................} Function TIMGUI.ScreenToWorldY(Const sy : Integer) : Integer; Begin Result := FOriginY + sy * FDownDir; End; with the GUI screen, I assume that the top left is 0,0 and the bottom right is (width,height) just like in windows. Now if I want to draw a button, I just do this: (x,y) +-------+ | | | | +-------+ (x+w,y+h) Procedure FIMGUI.DrawRadioButton(x,y,w,h : Integer; text : AnsiString); Begin mx := x + h Div 2; my := y + h Div 2; r := h Div 2; x1 := ScreenToWorldX(mx-r); y1 := ScreenToWorldY(my-r); x2 := ScreenToWorldX(mx+r); y2 := ScreenToWorldY(my+r); {...} // radio button background DrawRoundedRect(x1,y1, x2,y2, 0,r,cLineWidth, FBackgroundColor.r, FBackgroundColor.g, FBackgroundColor.b, FBackgroundColor.a, True,5); // radio button border DrawRoundedRect(x1,y1, x2,y2, 0,r,cLineWidth, FBorderColor.r, FBorderColor.g, FBorderColor.b, FBorderColor.a, False,5); r := Trunc(r * 0.65); x1 := ScreenToWorldX(mx-r); y1 := ScreenToWorldY(my-r); x2 := ScreenToWorldX(mx+r); y2 := ScreenToWorldY(my+r); // radio button active dot If active Then DrawRoundedRect(x1,y1, x2,y2, 0,r,cLineWidth, FBorderColor.r, FBorderColor.g, FBorderColor.b, FBorderColor.a, True,5); If text = '' Then Exit; If font = Nil Then Exit; FontH := font.MaxHeight; FontX := ScreenToWorldX(x+h+4); FontY := ScreenToWorldY(my - FontH Div 2); glEnable(GL_TEXTURE_2D); If FUIState.HotItem = id Then glColor4fv(@FHotColor) Else glColor4fv(@FFontColor); font.Draw(FontX,FontY,text,0); {...} End; I hope this helps? cheers, Paul

From: "Graeme Geldenhuys" To: "FPC-Pascal users discussions" Sent: Thursday, October 29, 2009 7:51 PM Subject: Re: [fpc-pascal] X, Y co-ordinate system under OS/2 > On 29/10/2009, Juha Manninen wrote: >> >> If done right, the code doing coordinate conversion should be in library >> Canvas class, not in application code. > > That's how I would have implemented in it fpGUI as well. The higher > level code uses x, y as normal. The drawing backend code does > conversions if needed. > > That's how I handle differences between Windows GDI API and XLib API. > > -- > Regards, > - Graeme - Very good points, and I completely agree :) I was only doing a quick "hack" so I could get something working in a short time ;) BTW, I found these very interesting articles about IMGUI (Immediate Mode GUI) systems (which I am using in my game): http://www.johno.se/book/imgui.html http://sol.gfxile.net/imgui/index.html and a forum about IMGUs http://www.mollyrocket.com/forums/viewforum.php?f=10 Perhaps this might help someone, except maybe Graeme "fpGUI" Geldenhuys LOL! ;P cheers, Paul