Merge pull request #16 from bcvery1/master

Line collision

community/line-collisions/README.md

@@ -0,0 +1,12 @@
+# Line Collisions
+Line collisions is a basic example of how to detect line collisions with a rectangle.
+
+![Screenshot](lineCollisionScreenshot.png)
+
+## Instructions
+You can set the rectangle position using a left-click of the mouse.
+
+You can set the line position with two right-clicks of the mouse; the first right-click will set the beginning of the
+line the second will set the end of the line.
+
+Any intersection points where the rectangle and line intersection will appear as red dots. 

community/line-collisions/main.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"image/color"
+
+	"github.com/faiface/pixel"
+	"github.com/faiface/pixel/imdraw"
+	"github.com/faiface/pixel/pixelgl"
+)
+
+// These hold the state of whether we're placing the first or second point of the line.
+const (
+	clickLineA = iota
+	clickLineB
+)
+
+var (
+	winBounds = pixel.R(0, 0, 1024, 768)
+
+	r = pixel.R(10, 10, 70, 50)
+	l = pixel.L(pixel.V(20, 20), pixel.V(100, 30))
+
+	clickLine = clickLineA
+)
+
+func run() {
+	cfg := pixelgl.WindowConfig{
+		Title:  "Line collision",
+		Bounds: winBounds,
+		VSync:  true,
+	}
+
+	win, err := pixelgl.NewWindow(cfg)
+	if err != nil {
+		panic(err)
+	}
+
+	imd := imdraw.New(nil)
+
+	for !win.Closed() {
+		win.Clear(color.RGBA{R: 23, G: 39, B: 58, A: 125})
+		imd.Clear()
+
+		// When mouse left-click, move the rectangle so its' center is at the mouse position
+		if win.JustPressed(pixelgl.MouseButtonLeft) {
+			rectToMouse := r.Center().To(win.MousePosition())
+			r = r.Moved(rectToMouse)
+		}
+
+		// When mouse right-click, set either the beginning or end of the line.
+		if win.JustPressed(pixelgl.MouseButtonRight) {
+			if clickLine == clickLineA {
+				// Set the beginning of the line to the mouse position.
+				// To make it clearer to the user, set the end position 1 pixel (in each direction) away from the first
+				// point.
+				l = pixel.L(win.MousePosition(), win.MousePosition().Add(pixel.V(1, 1)))
+				clickLine = clickLineB
+			} else {
+				// Set the end point of the line.
+				l = pixel.L(l.A, win.MousePosition())
+				clickLine = clickLineA
+			}
+		}
+
+		// Draw the rectangle.
+		imd.Color = color.Black
+		imd.Push(r.Min, r.Max)
+		imd.Rectangle(3)
+
+		// Draw the line.
+		imd.Color = color.RGBA{R: 10, G: 10, B: 250, A: 255}
+		imd.Push(l.A, l.B)
+		imd.Line(3)
+
+		imd.Color = color.RGBA{R: 250, G: 10, B: 10, A: 255}
+		// Draw any intersection points.
+		for _, i := range r.IntersectionPoints(l) {
+			imd.Push(i)
+			imd.Circle(4, 0)
+		}
+
+		imd.Draw(win)
+		win.Update()
+	}
+}
+
+func main() {
+	pixelgl.Run(run)
+}