From 3bab08a0a6aa46a5617d9acba33a57ded7b49078 Mon Sep 17 00:00:00 2001
From: Sander Schobers <sander@schobers.eu>
Date: Sat, 23 May 2020 08:20:04 +0200
Subject: [PATCH] Added support for rendering a partial texture.

---
 allg5ui/renderer.go | 22 ++++++++++++++++++++--
 sdlui/renderer.go   | 30 ++++++++++++++++++++++--------
 ui/drawoptions.go   |  3 ++-
 3 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/allg5ui/renderer.go b/allg5ui/renderer.go
index 7d77db1..3b9a43e 100644
--- a/allg5ui/renderer.go
+++ b/allg5ui/renderer.go
@@ -237,7 +237,10 @@ func (r *Renderer) DrawTexture(texture ui.Texture, p geom.RectangleF32) {
 }
 
 func (r *Renderer) DrawTextureOptions(texture ui.Texture, p geom.RectangleF32, opts ui.DrawOptions) {
-	bmp := r.mustGetBitmap(texture)
+	bmp, ok := r.mustGetSubBitmap(texture, opts.Source)
+	if ok {
+		defer bmp.Destroy()
+	}
 	x, y := snap(p.Min)
 	var o allg5.DrawOptions
 	if opts.Tint != nil {
@@ -259,7 +262,10 @@ func (r *Renderer) DrawTexturePoint(texture ui.Texture, p geom.PointF32) {
 }
 
 func (r *Renderer) DrawTexturePointOptions(texture ui.Texture, p geom.PointF32, opts ui.DrawOptions) {
-	bmp := r.mustGetBitmap(texture)
+	bmp, ok := r.mustGetSubBitmap(texture, opts.Source)
+	if ok {
+		defer bmp.Destroy()
+	}
 	var o allg5.DrawOptions
 	if opts.Tint != nil {
 		tint := newColor(opts.Tint)
@@ -281,6 +287,18 @@ func (r *Renderer) mustGetBitmap(t ui.Texture) *allg5.Bitmap {
 	return texture.bmp
 }
 
+func (r *Renderer) mustGetSubBitmap(t ui.Texture, source *geom.RectangleF32) (*allg5.Bitmap, bool) {
+	texture, ok := t.(*texture)
+	if !ok {
+		panic("texture must be created on same renderer")
+	}
+	if source == nil {
+		return texture.bmp, false
+	}
+	src := source.ToInt()
+	return texture.bmp.Sub(src.Min.X, src.Min.Y, src.Dx(), src.Dy()), true
+}
+
 func (r *Renderer) Rectangle(rect geom.RectangleF32, c color.Color, thickness float32) {
 	minX, minY := snap(rect.Min)
 	maxX, maxY := snap(rect.Max)
diff --git a/sdlui/renderer.go b/sdlui/renderer.go
index fe38d39..8d39454 100644
--- a/sdlui/renderer.go
+++ b/sdlui/renderer.go
@@ -311,11 +311,17 @@ func (r *Renderer) DrawTextureOptions(t ui.Texture, dst geom.RectangleF32, opts
 	if !ok {
 		return
 	}
-	width, height, err := texture.Size()
-	if err != nil {
-		return
+	var source sdl.Rect
+	if opts.Source != nil {
+		source = RectAbs(int32(opts.Source.Min.X), int32(opts.Source.Min.Y), int32(opts.Source.Max.X), int32(opts.Source.Max.Y))
+	} else {
+		width, height, err := texture.Size()
+		if err != nil {
+			return
+		}
+		source = Rect(0, 0, width, height)
 	}
-	r.drawTexture(texture, Rect(0, 0, width, height), RectAbs(int32(dst.Min.X), int32(dst.Min.Y), int32(dst.Max.X), int32(dst.Max.Y)), opts)
+	r.drawTexture(texture, source, RectAbs(int32(dst.Min.X), int32(dst.Min.Y), int32(dst.Max.X), int32(dst.Max.Y)), opts)
 }
 
 func (r *Renderer) DrawTexturePoint(t ui.Texture, dst geom.PointF32) {
@@ -327,11 +333,19 @@ func (r *Renderer) DrawTexturePointOptions(t ui.Texture, dst geom.PointF32, opts
 	if !ok {
 		return
 	}
-	width, height, err := texture.Size()
-	if err != nil {
-		return
+	var source, destination sdl.Rect
+	if opts.Source != nil {
+		source = RectAbs(int32(opts.Source.Min.X), int32(opts.Source.Min.Y), int32(opts.Source.Max.X), int32(opts.Source.Max.Y))
+		destination = Rect(int32(dst.X), int32(dst.Y), source.W, source.H)
+	} else {
+		width, height, err := texture.Size()
+		if err != nil {
+			return
+		}
+		source = Rect(0, 0, width, height)
+		destination = Rect(int32(dst.X), int32(dst.Y), width, height)
 	}
-	r.drawTexture(texture, Rect(0, 0, width, height), Rect(int32(dst.X), int32(dst.Y), width, height), opts)
+	r.drawTexture(texture, source, destination, opts)
 }
 
 func (r *Renderer) FillRectangle(rect geom.RectangleF32, c color.Color) {
diff --git a/ui/drawoptions.go b/ui/drawoptions.go
index bd5f925..a222af8 100644
--- a/ui/drawoptions.go
+++ b/ui/drawoptions.go
@@ -7,7 +7,8 @@ import (
 )
 
 type DrawOptions struct {
-	Tint color.Color
+	Source *geom.RectangleF32
+	Tint   color.Color
 }
 
 func ScaleToHeight(size geom.PointF32, height float32) (*geom.PointF32, float32) {