From 4ab710eba1708966f8ae9e637deafa5be060b6d5 Mon Sep 17 00:00:00 2001
From: xengineering <mail2xengineering@protonmail.com>
Date: Tue, 25 May 2021 12:51:50 +0200
Subject: Implement Home View

---
 app.go      | 13 ++++++++-----
 geometry.go | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 main.go     |  2 +-
 3 files changed, 56 insertions(+), 6 deletions(-)

diff --git a/app.go b/app.go
index 0591be9..22548a3 100644
--- a/app.go
+++ b/app.go
@@ -18,11 +18,14 @@ const (
 type App struct {
 	window *glfw.Window
 	graphics *Graphics
+	stl *StlModel
+	homeTrafo mgl32.Mat4
 }
 
-func newApp() App {
+func newApp(stl *StlModel) App {
 
 	var app App = App{}
+	app.stl = stl
 	var err error
 
 	log.Println("GLFW init")
@@ -44,6 +47,8 @@ func newApp() App {
 	}
 	app.window.MakeContextCurrent()
 
+	app.homeTrafo = stl.surface.getHomeView()
+
 	return app
 }
 
@@ -52,10 +57,8 @@ func (application *App) handle() {
 	application.window.SwapBuffers()
 
 	// generate and set transformation
-	var scale float32 = 0.01
-	trafo := mgl32.Ident4()
-	trafo = trafo.Mul4(mgl32.HomogRotate3D(float32(glfw.GetTime()) * 3, mgl32.Vec3{0, 1, 1}))
-	trafo = trafo.Mul4(mgl32.Scale3D(scale, scale, scale))
+	trafo := application.homeTrafo
+	trafo = mgl32.HomogRotate3D(float32(glfw.GetTime()) * 3, mgl32.Vec3{0, 1, 0}).Mul4(trafo)  // apply time-based rotation
 	application.graphics.setTrafo(trafo)
 }
 
diff --git a/geometry.go b/geometry.go
index 04896dc..1fc516a 100644
--- a/geometry.go
+++ b/geometry.go
@@ -2,6 +2,10 @@
 
 package main
 
+import (
+	"github.com/go-gl/mathgl/mgl32"
+)
+
 // representation of a three-dimensional point in space
 type Point struct {
 	scalars [3]float32  // x = scalars[0], y = scalars[1], z = scalars[2]
@@ -17,3 +21,46 @@ type Surface struct {
 	triangles []*Triangle
 }
 
+// return a transformation to view the whole centered surface
+func (s Surface) getHomeView() mgl32.Mat4 {
+
+	// evaluating the smallest and biggest values for x,y,z of the surface
+	var min,max [3]float32
+	for _,triangle := range(s.triangles) {
+		for _,point := range(triangle.points) {
+			for index,_ := range(min) {
+				if point.scalars[index] < min[index] {
+					min[index] = point.scalars[index]
+				}
+				if point.scalars[index] > max[index] {
+					max[index] = point.scalars[index]
+				}
+			}
+		}
+	}
+
+	// calculate center point
+	var center Point
+	for index,_ := range(min) {
+		center.scalars[index] = (min[index] + max[index]) / 2
+	}
+
+	// calculate zoom
+	var zoom,zoomX,zoomY float32
+	const fillFactor float32 = 0.8
+	zoomX = (2 / (max[0] - min[0])) * fillFactor
+	zoomY = (2 / (max[1] - min[1])) * fillFactor
+	if zoomX > zoomY {
+		zoom = zoomY
+	} else {
+		zoom = zoomX
+	}
+
+	// calculate and return transformation
+	var trafo mgl32.Mat4 = mgl32.Ident4()
+	trafo = mgl32.Translate3D(-center.scalars[0], -center.scalars[1], -center.scalars[2]).Mul4(trafo)
+	trafo = mgl32.Scale3D(zoom, zoom, zoom).Mul4(trafo)
+
+	return trafo
+}
+
diff --git a/main.go b/main.go
index 1bf0b9d..e74cd1f 100644
--- a/main.go
+++ b/main.go
@@ -28,7 +28,7 @@ func main() {
 	vertices = stl.toVertices()
 
 	// initialize application (includes GLFW/window)
-	var app App = newApp()
+	var app App = newApp(&stl)
 	defer app.terminate()  // GLFW needs to be terminated!
 
 	// initialize graphics
-- 
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