How to draw hatches

Hi,

there is something more to say. Because hatch or not hatch is a question of orientation.

My first example shows a normal drawn box and for clipping a path consisting of a circle and a hatch-box in it. Here the source:
QP.SetOrigin(0); // Bottomleft
QP.SetMeasurementUnits(1); // Millimeter
QP.SetPageDimensions(210, 297);

QP.SetLineWidth(0.1);
QP.SetLineColor(1, 0, 0);
QP.SetFillColor(1, 1, 0);
x0 := 25; x1 := 175;
y0 := 170; y1 := 270;
r := 70;
// 1. draw without clipping
QP.DrawBox(x0, y1, x1-x0, y1-y0, 1);
QP.DrawCircle((x0+x1)/2, y1-r, r, 0);

QP.SaveState; // for later use without clipping
// 2. define clipping path
QP.StartPath((x0+x1)/2, y1);
QP.AddArcToPath((x0+x1)/2, y1-r, 360); // the "normal" path for clipping
// 3. hatch-box-building
// hatch or not hatch is a question of orientation
QP.MovePath(x0+20, y0+75); // upper left corner
QP.AddLineToPath(x0+20, y0+50); // lower left
QP.AddLineToPath(x0+50, y0+50); // lower right
QP.AddLineToPath(x0+50, y0+75); // upper right
QP.AddLineToPath(x0+20, y0+75); // close hatch, important!
QP.SetClippingPath;
// 4. draw clipped things
// it will be drawn only inside the first circle and outside our hatchbox
QP.DrawBox(x0, y1, x1-x0, y1-y0, 0);
for i:=0 to 52 do QP.DrawLine(x1-i*5, y0, x1, y0+i*5);
QP.SetFillColor(0, 1, 0);
QP.DrawCircle(x0+50, y0+75, 10, 2);

QP.LoadState; // stop clipping from here

QP.SetLineColor(0, 0, 0);
QP.DrawLine(x0, y0, (x0+x1)/2, y1);

The second example is more interessting. Using four lines two triangles are builded, but only one of them becomes to be hatch.

That's so because of orientation during AddLineToPath-sequence.

Wandering from P1 over P2 to P3 upper triangle is ever on your right side. But the other Triangle is on the way from P3 over P4 to P1 on left side. Areas on right side are are parts of the path, but areas on left side dont't belong to path, they are hatches.

Source for this:
x0 := 100; y1 := y0-50; y0 := 20; r := 30;
QP.SaveState; // for later use without clipping
QP.StartPath(x0-r-5, y1+5);
//first a box as clipping area
QP.AddLineToPath(x0+2*r, y1);
QP.AddLineToPath(x0+2*r, y0-1);
QP.AddLineToPath(x0-r, y0-1);
QP.AddLineToPath(x0-r, y1);
// and now a special kind of half hatch
QP.MovePath(x0, y1);
QP.AddLineToPath(x0+r, y1);
QP.AddLineToPath(x0-r, y0);
QP.AddLineToPath(x0+r, y0);
QP.AddLineToPath(x0, y1);
QP.SetClippingPath;
QP.DrawBox(x0-r, y1, 2*r, y1-y0, 1);
// show hatch construction
QP.SetLineColor(0, 0, 0);
QP.SetLineWidth(1.0);
QP.DrawLine(x0, y1, x0+r, y1); // show the contour
QP.DrawLine(x0+r, y1, x0-r, y0);
QP.DrawLine(x0-r, y0, x0+r, y0);
QP.DrawLine(x0+r, y0, x0, y1);

QP.LoadState; // stop clipping now again
QP.DrawText(x0, y1+2, 'P1');
QP.DrawText(x0+r, y1+2, 'P2');
QP.DrawText(x0-r, y0-5, 'P3');
QP.DrawText(x0+r, y0-5, 'P4');

Cheers,
Werner

Edited by edvoigt - 03 Feb 12 at 8:20PM

Author	Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic
kaiken1987 Members Profile Find Members Posts Beginner Joined: 27 Jan 12 Location: United States Status: Offline Points: 5	Post Options Post Reply Quote kaiken1987 Report Post Thanks(0) Quote Reply Topic: How to draw hatches Posted: 31 Jan 12 at 2:56PM
	I'm trying to find a way to draw filled polygons with holes in them, something like the widows GDI polypolygon function. The only way I've been able to figure out is to call GetCanvasDC, RenderToDC, use the polypolygon function and then call LoadFromCanvasDC. That seems terribly slow and inefficient and I assume the must be a better way then that.

AndrewC Members Profile Find Members Posts Moderator Group Joined: 08 Dec 10 Location: Geelong, Aust Status: Offline Points: 841	Post Options Post Reply Quote AndrewC Report Post Thanks(0) Quote Reply Posted: 01 Feb 12 at 8:25AM
	Here is some code to draw a hollow star.. // Draw a hollow star QP.SetFillColor(1, 0, 0); QP.SetLineColor(0, 1, 0); QP.StartPath(100, 60); QP.AddLineToPath(306, 600); QP.AddLineToPath(512, 60); QP.AddLineToPath(20, 400); QP.AddLineToPath(592, 400); QP.ClosePath(); QP.DrawPathEvenOdd(2); // Draw a hollow donut QP.NewPage(); QP.SetFillColor(1, 0, 0); QP.SetLineColor(0, 1, 0); QP.StartPath(100, 200); QP.AddArcToPath(200, 200, 360); QP.MovePath(150, 200); QP.AddArcToPath(200, 200, 360); QP.ClosePath(); QP.DrawPathEvenOdd(2);

kaiken1987 Members Profile Find Members Posts Beginner Joined: 27 Jan 12 Location: United States Status: Offline Points: 5	Post Options Post Reply Quote kaiken1987 Report Post Thanks(0) Quote Reply Posted: 02 Feb 12 at 1:58PM
	Thank you that worked for me very well.

edvoigt Members Profile Find Members Posts Senior Member Joined: 26 Mar 11 Location: Berlin, Germany Status: Offline Points: 111	Post Options Post Reply Quote edvoigt Report Post Thanks(0) Quote Reply Posted: 03 Feb 12 at 8:18PM
	Hi, there is something more to say. Because hatch or not hatch is a question of orientation. My first example shows a normal drawn box and for clipping a path consisting of a circle and a hatch-box in it. Here the source: QP.SetOrigin(0); // Bottomleft QP.SetMeasurementUnits(1); // Millimeter QP.SetPageDimensions(210, 297); QP.SetLineWidth(0.1); QP.SetLineColor(1, 0, 0); QP.SetFillColor(1, 1, 0); x0 := 25; x1 := 175; y0 := 170; y1 := 270; r := 70; // 1. draw without clipping QP.DrawBox(x0, y1, x1-x0, y1-y0, 1); QP.DrawCircle((x0+x1)/2, y1-r, r, 0); QP.SaveState; // for later use without clipping // 2. define clipping path QP.StartPath((x0+x1)/2, y1); QP.AddArcToPath((x0+x1)/2, y1-r, 360); // the "normal" path for clipping // 3. hatch-box-building // hatch or not hatch is a question of orientation QP.MovePath(x0+20, y0+75); // upper left corner QP.AddLineToPath(x0+20, y0+50); // lower left QP.AddLineToPath(x0+50, y0+50); // lower right QP.AddLineToPath(x0+50, y0+75); // upper right QP.AddLineToPath(x0+20, y0+75); // close hatch, important! QP.SetClippingPath; // 4. draw clipped things // it will be drawn only inside the first circle and outside our hatchbox QP.DrawBox(x0, y1, x1-x0, y1-y0, 0); for i:=0 to 52 do QP.DrawLine(x1-i5, y0, x1, y0+i5); QP.SetFillColor(0, 1, 0); QP.DrawCircle(x0+50, y0+75, 10, 2); QP.LoadState; // stop clipping from here QP.SetLineColor(0, 0, 0); QP.DrawLine(x0, y0, (x0+x1)/2, y1); The second example is more interessting. Using four lines two triangles are builded, but only one of them becomes to be hatch. That's so because of orientation during AddLineToPath-sequence. Wandering from P1 over P2 to P3 upper triangle is ever on your right side. But the other Triangle is on the way from P3 over P4 to P1 on left side. Areas on right side are are parts of the path, but areas on left side dont't belong to path, they are hatches. Source for this: x0 := 100; y1 := y0-50; y0 := 20; r := 30; QP.SaveState; // for later use without clipping QP.StartPath(x0-r-5, y1+5); //first a box as clipping area QP.AddLineToPath(x0+2r, y1); QP.AddLineToPath(x0+2r, y0-1); QP.AddLineToPath(x0-r, y0-1); QP.AddLineToPath(x0-r, y1); // and now a special kind of half hatch QP.MovePath(x0, y1); QP.AddLineToPath(x0+r, y1); QP.AddLineToPath(x0-r, y0); QP.AddLineToPath(x0+r, y0); QP.AddLineToPath(x0, y1); QP.SetClippingPath; QP.DrawBox(x0-r, y1, 2*r, y1-y0, 1); // show hatch construction QP.SetLineColor(0, 0, 0); QP.SetLineWidth(1.0); QP.DrawLine(x0, y1, x0+r, y1); // show the contour QP.DrawLine(x0+r, y1, x0-r, y0); QP.DrawLine(x0-r, y0, x0+r, y0); QP.DrawLine(x0+r, y0, x0, y1); QP.LoadState; // stop clipping now again QP.DrawText(x0, y1+2, 'P1'); QP.DrawText(x0+r, y1+2, 'P2'); QP.DrawText(x0-r, y0-5, 'P3'); QP.DrawText(x0+r, y0-5, 'P4'); Cheers, Werner Edited by edvoigt - 03 Feb 12 at 8:20PM