can we translate the coordinate when drawing in a paintbox
lazarus / 39-Graphics

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vkhoa · 2014-06-18 10:05

can we translate the coordinate or rotate it?

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Blaazen · 2014-06-18 10:22

Coordinate of what?

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vkhoa · 2014-06-18 12:17

sorry for the question is not clear,
it's the coordinate of a canvas of a paintbox
I want to paint in the relative coordinate

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Blaazen · 2014-06-18 12:32

You probably mean one of these functions:
Code: [Select]  ControlToScreen();
  ScreenToControl();
  ClientToScreen();
  ScreenToClient();
  ClientToParent();
  ParentToClient();
For example
Code: [Select]procedure TForm1.Button1Click(Sender: TObject);
var aPoint: TPoint;
begin
  aPoint:=Button1.ControlToScreen(Point(0, 0));
  Writeln(aPoint.X, ' ', aPoint.Y);
end;will write absolute coordinates of Button1 (from Top-Left corner
of the screen).

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vkhoa · 2014-06-19 00:24

no, that's not what I mean, the coordinate I say is in the canvas ,
the top left corner of paintbox is(0,0), now I want the (0,0) is at
(50,50)
what I want is something like this
Code: [Select]paintbox1.canvas.line(0,0,200,100);//this line will draw
a line from 0,0 to 200,100
translate(50,50);                            //is there some method
like this?it translate the coorddinate by 50,50
paintbox1.canvas.line(0,0,100,60);//now this line will draw a line
from 50,50 to 150,110

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taazz · 2014-06-19 00:44

no but it is easy to write something like this. there is a proof of
concept canvas in my simplegraph port to lazarus at
http://sourceforge.net/projects/evssimplegraph/ unit usimplegraph it
has 2 canvas based implementations one based on TCustomCanvas and one
based on TControlCanvas they are both there because I experiment with
different ways to replace the control's default canvas, the one used
in the component it self is the TEvsGraphCanvas which is based on the
TcontrolCanvas, you can look on the TEvsSimpleGraph constructor for
the code used to replace the existing TControlCanvas.

Be warned only the translation is active no zoom or rotation is
supported it requires a bit of work to add those two.

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engkin · 2014-06-19 02:43

Quote from: vkhoa on June 19, 2014, 02:24:20 amno, that's not what I
mean, the coordinate I say is in the canvas , the top left corner of
paintbox is(0,0), now I want the (0,0) is at (50,50)
what I want is something like this
Code: [Select]paintbox1.canvas.line(0,0,200,100);//this line will draw
a line from 0,0 to 200,100
translate(50,50);                            //is there some method
like this?it translate the coorddinate by 50,50
paintbox1.canvas.line(0,0,100,60);//now this line will draw a line
from 50,50 to 150,110Windows supports it:
Code: [Select]uses
  .., Windows;
...
var
  xf:XFORM;
begin
  //Enable world transformation
  SetGraphicsMode(Canvas.Handle, GM_ADVANCED);

  //Prepare some transformation structure
  //based on:
  //x' = x * eM11 + y * eM21 + eDx,
  //y' = x * eM12 + y * eM22 + eDy,
  xf.eM11:=1;
  xf.eM22:=1;
  xf.eDx:=50;
  xf.eDy:=50;

  //before applying transformation
  Canvas.Line(0,0,200,100);

  //apply wanted transformation
  SetWorldTransform(Canvas.Handle, xf);
  Canvas.Line(0,0,100,60);
end;

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vkhoa · 2014-06-19 08:29

thanks for both replies
I have tried engkin example, it worked but...
I was curious about the default value of the properties em12,em21
(thinking it is equal to 0 when I guess em11,em22 is the scale rate)
so I coded this
Code: [Select]Procedure TForm1.PaintBox1Paint(Sender: TObject);
var xf:xform;
Begin
  //Enable world transformation
   SetGraphicsMode(paintbox1.Canvas.Handle, GM_ADVANCED);

   //Prepare some transformation structure
  //based on:
  //x' = x * eM11 + y * eM21 + eDx,
  //y' = x * eM12 + y * eM22 + eDy,
  xf.eM11:=3;
  xf.eM22:=1;
  xf.eDx:=50;
  xf.eDy:=50;

  //before applying transformation
  paintbox1.Canvas.Line(0,0,200,100);
  paintbox1.Canvas.TextOut(0,0,floattostr(xf.eM12)+',
'+floattostr(xf.eM21));
  //apply wanted transformation
  SetWorldTransform(paintbox1.Canvas.Handle, xf);
  paintbox1.Canvas.Line(0,0,100,60);
  paintbox1.Canvas.Font.Color:=clblue;
  paintbox1.Canvas.TextOut(0,0,floattostr(xf.eM12)+',
'+floattostr(xf.eM21));
end;  the first textout it displayed corectly, but the second
textout(after setworldtransform) it displayed nothing,i also changed
the text parameters to a constance string but it still did not
display, is it an issue
and another question, why em12,em21 is a very small positive value but
not equal to 0

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engkin · 2014-06-19 12:21

Quote from: vkhoa on June 19, 2014, 10:29:56 amI was curious about the
default value of the properties em12,em21 (thinking it is equal to 0
when I guess em11,em22 is the scale rate)
..
why em12,em21 is a very small positive value but not equal to 0
Global variables are initialized to zero by default (and they reside
on the heap). Local function variables are *not* initialized and hold
random values (they reside on the stack) and you need to initialize
them.

Add the following line to the beginning of your code:
Code: [Select]Procedure TForm1.PaintBox1Paint(Sender: TObject);
var
  xf:xform;
Begin
  ZeroMemory(@xf, SizeOf(xf));  //<------ This line

  //Enable world transformation
   SetGraphicsMode(paintbox1.Canvas.Handle, GM_ADVANCED);
...

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vkhoa · 2014-06-20 09:54

thanks, I got it.