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Posted on 1998-09-02
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this is a follow up to my question titled 'Draw Graphs'...

commercial toolkits are out of the question bcos my school project does not have a budget for it (such toolkits cost money rite??)

pls forgive me for i have just started learning VC++.... so can you kindly explain in more details the following:

1) Drawing of grids using the LineTo, TextOut etc etc functions.

2) For the program to generate the graph... let say i got two variables, theta and displacement, i will calculate the displacement at certain interval of theta. eg, at theta equal to 5, 10, 15, 20.... displacements are d1, d2, d3, d4. as such i would have the various pts. question is, how do i map this points into the grid i have drawn?? also, how to i join this various pts up after i mapped them into the grid i drawn??

the project gonna due very soon and i just can't seem to solve the problem. your help is very much appreciated. thanz in advance.
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Question by:bi7206327
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by:bi7206327
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snoegler earned 80 total points
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This is for a school assignment - so we are not allowed here to show you entire code.
I think you need basically help with the drawing - and not with the logic behind it.
So i'll post here some code which may help you. A short explanation:

The class gridInfo describes the grid to draw.
The function check_grid() makes sure that the grid data is valid.
The function grid_to_coord() converts a grid coordinate into a screen coordinate
(i think that's what you wanted, but i'm not sure)
wrap_value() 'rounds' the given value to the next given number.
The function paint_grid() paints the grid.

I think you should implement the function which actually draws the graph by yourself -
it is not hard to do, just take you some time, a block of paper and you should be able
to make it.


class gridInfo {
  public:
  double  x_min;
  double  x_max;
  double  y_min;
  double  y_max;
  double delta_x_intense; // intense coordinate lines, for example 10
  double delta_y_intense; // which would mean that -20;-10;0;10;20;...
  double delta_x_light; // light coordinate lines, for example 1;
  double delta_y_light;
};

void check_grid(gridInfo& gi)
{
  ASSERT( (gi.x_max-gi.x_min)>0 );
  ASSERT( (gi.y_max-gi.y_min)>0 );
}

void grid_to_coord(CRect& rcPaint,gridInfo& gi,double grid_x,double grid_y,
                                  int& coord_x,int& coord_y)
{
  check_grid(gi);
  grid_x-=gi.x_min;
  grid_y-=gi.y_min;
  ASSERT(grid_x>=0); ASSERT(grid_y>=0);
  // 0<=grid_x/y
  grid_x/=(gi.x_max-gi.x_min);
  grid_y/=(gi.y_max-gi.y_min);
  // 0<=grix_x/y<=1
  // by standard, the positive values grow into negative screen coordinates ->
  grid_y=1-grid_y;
  // now map these [0..1]|[0..1] coordinates in the target (screen) rectangle
  coord_x=( grid_x*((double)rcPaint.Width()) )+rcPaint.left;
  coord_y=( grid_y*((double)rcPaint.Height()) )+rcPaint.top;
  // rcPaint.left<=coord_x<=rcPaint.right
  // rcPaint.top<=coord_y<=rcPaint.bottom
}

double wrap_value(double value,double mod,BOOL wrapUp)
{
  BOOL usePositive; // value+ or value-? (see below)
  // if value is less than zero, fmod()<0 too!
  usePositive      =wrapUp;
  if(value<0) wrapUp=wrapUp?FALSE:TRUE;
  if(usePositive)
    value=value+fmod(value,mod);
  else
    value=value-fmod(value,mod);
  return value;
}
      

void paint_grid(CDC& dc,CRect& rcPaint,gridInfo& gi)
{
  CPen intense_line(PS_SOLID,1,RGB(255,255,255));
  CPen light_line(PS_SOLID,1,RGB(128,128,128));
  CPen *old;

  double counter;
  dc.FillSolidRect(rcPaint,0);
  old=dc.SelectObject(&light_line); // select light line pen, save old selected pen
/*** draw light x-axis lines ***/
  for(counter=wrap_value(gi.x_min,gi.delta_x_light,FALSE);
    counter<=wrap_value(gi.x_max,gi.delta_x_light,TRUE);
    counter+=gi.delta_x_light) {
    int sx,sy;
    grid_to_coord(rcPaint,gi,counter,0,sx,sy);
    dc.MoveTo(sx,rcPaint.top);
    dc.LineTo(sx,rcPaint.bottom);
  }
/*** draw light y-axis lines ***/
  for(counter=wrap_value(gi.y_min,gi.delta_y_light,FALSE);
    counter<=wrap_value(gi.y_max,gi.delta_y_light,TRUE);
    counter+=gi.delta_y_light) {
    int sx,sy;
    grid_to_coord(rcPaint,gi,0,counter,sx,sy);
    dc.MoveTo(rcPaint.left,sy);
    dc.LineTo(rcPaint.right,sy);
  }
  dc.SelectObject(&intense_line); // select intense line pen
/*** draw intense x-axis lines ***/
  for(counter=wrap_value(gi.x_min,gi.delta_x_intense,FALSE);
    counter<=wrap_value(gi.x_max,gi.delta_x_intense,TRUE);
    counter+=gi.delta_x_intense) {
    int sx,sy;
    grid_to_coord(rcPaint,gi,counter,0,sx,sy);
    dc.MoveTo(sx,rcPaint.top);
    dc.LineTo(sx,rcPaint.bottom);
  }
/*** draw intense y-axis lines ***/
  for(counter=wrap_value(gi.y_min,gi.delta_y_intense,FALSE);
    counter<=wrap_value(gi.y_max,gi.delta_y_intense,TRUE);
    counter+=gi.delta_y_intense) {
    int sx,sy;
    grid_to_coord(rcPaint,gi,0,counter,sx,sy);
    dc.MoveTo(rcPaint.left,sy);
    dc.LineTo(rcPaint.right,sy);
  }
}

To see a fast example, create a SDI-app,  and put this in the CView::OnDraw() function:
(of course, you have to place to code above somewhere)

gridInfo testgrid;
CRect testrect;

testgrid.x_min=-20;
testgrid.x_max=20;
testgrid.y_min=-20;
testgrid.y_max=20;
testgrid.delta_x_intense=10;
testgrid.delta_y_intense=10;
testgrid.delta_x_light=1;
testgrid.delta_y_light=1;
testrect=CRect(50,50,250,250);
paint_grid(*pDC,testrect,testgrid);

What's missing are labels and the graph :)
I hope this helped a bit
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