From 23115b8a0fda133b9030ad3a2107fb461ceed970 Mon Sep 17 00:00:00 2001
From: Sander Schobers <sander@schobers.eu>
Date: Fri, 22 May 2020 17:42:02 +0200
Subject: [PATCH] Added support for rendering text to a texture.

---
 allg5ui/renderer.go |  4 ++++
 sdlui/renderer.go   | 49 ++++++++++++++++++++++++++++++---------------
 ui/fonts.go         |  9 +++++++++
 ui/renderer.go      | 17 ++++++++++++++++
 4 files changed, 63 insertions(+), 16 deletions(-)

diff --git a/allg5ui/renderer.go b/allg5ui/renderer.go
index ed53cb8..7d77db1 100644
--- a/allg5ui/renderer.go
+++ b/allg5ui/renderer.go
@@ -356,6 +356,10 @@ func (r *Renderer) TextAlign(font ui.Font, p geom.PointF32, c color.Color, t str
 	r.text(font, p, c, t, alignment)
 }
 
+func (r *Renderer) TextTexture(font ui.Font, color color.Color, text string) (ui.Texture, error) {
+	return ui.TextTexture(r, font, color, text)
+}
+
 // Utility functions
 
 func eventWait(eq *allg5.EventQueue, wait bool) allg5.Event {
diff --git a/sdlui/renderer.go b/sdlui/renderer.go
index 7d4ef86..fe38d39 100644
--- a/sdlui/renderer.go
+++ b/sdlui/renderer.go
@@ -264,6 +264,19 @@ func (r *Renderer) createTexture(source ui.ImageSource, keepSource bool) (ui.Tex
 	return &Texture{texture}, nil
 }
 
+func (r *Renderer) createTextureTarget(w, h float32) (*Texture, error) {
+	format, err := r.window.GetPixelFormat()
+	if err != nil {
+		return nil, err
+	}
+	texture, err := r.renderer.CreateTexture(format, sdl.TEXTUREACCESS_TARGET, int32(w), int32(h))
+	if err != nil {
+		return nil, err
+	}
+	texture.SetBlendMode(sdl.BLENDMODE_BLEND)
+	return &Texture{texture}, nil
+}
+
 func (r *Renderer) CreateTexture(source ui.ImageSource) (ui.Texture, error) {
 	return r.createTexture(source, true)
 }
@@ -277,16 +290,7 @@ func (r *Renderer) CreateTexturePath(path string, source bool) (ui.Texture, erro
 }
 
 func (r *Renderer) CreateTextureTarget(w, h float32) (ui.Texture, error) {
-	format, err := r.window.GetPixelFormat()
-	if err != nil {
-		return nil, err
-	}
-	texture, err := r.renderer.CreateTexture(format, sdl.TEXTUREACCESS_TARGET, int32(w), int32(h))
-	if err != nil {
-		return nil, err
-	}
-	texture.SetBlendMode(sdl.BLENDMODE_BLEND)
-	return &Texture{texture}, nil
+	return r.createTextureTarget(w, h)
 }
 
 func (r *Renderer) DefaultTarget() ui.Texture { return r }
@@ -408,21 +412,30 @@ func (r *Renderer) Target() ui.Texture {
 	return &Texture{target}
 }
 
-func (r *Renderer) Text(font ui.Font, p geom.PointF32, color color.Color, text string) {
-	f := font.(*Font)
-
+func (r *Renderer) text(font ui.Font, color color.Color, text string) (*Texture, error) {
+	f, ok := font.(*Font)
+	if !ok {
+		return nil, errors.New("font not created with renderer")
+	}
 	surface, err := f.RenderUTF8Blended(text, ColorSDL(color))
 	if err != nil {
-		return
+		return nil, err
 	}
 	defer surface.Free()
 	texture, err := r.renderer.CreateTextureFromSurface(surface)
+	if err != nil {
+		return nil, err
+	}
+	return &Texture{texture}, nil
+}
+
+func (r *Renderer) Text(font ui.Font, p geom.PointF32, color color.Color, text string) {
+	texture, err := r.text(font, color, text)
 	if err != nil {
 		return
 	}
 	defer texture.Destroy()
-
-	r.DrawTexturePoint(&Texture{texture}, p)
+	r.DrawTexturePoint(texture, p)
 }
 
 func (r *Renderer) TextAlign(font ui.Font, p geom.PointF32, color color.Color, text string, align ui.HorizontalAlignment) {
@@ -438,6 +451,10 @@ func (r *Renderer) TextAlign(font ui.Font, p geom.PointF32, color color.Color, t
 	}
 }
 
+func (r *Renderer) TextTexture(font ui.Font, color color.Color, text string) (ui.Texture, error) {
+	return r.text(font, color, text)
+}
+
 // Resources
 
 func (r *Renderer) Resources() ui.Resources { return r.resources }
diff --git a/ui/fonts.go b/ui/fonts.go
index 23140f5..9b650b3 100644
--- a/ui/fonts.go
+++ b/ui/fonts.go
@@ -1,6 +1,7 @@
 package ui
 
 import (
+	"fmt"
 	"image/color"
 
 	"opslag.de/schobers/geom"
@@ -68,3 +69,11 @@ func (f *Fonts) TextAlign(fontName string, p geom.PointF32, color color.Color, t
 	}
 	f.render.TextAlign(font, p, color, text, align)
 }
+
+func (f *Fonts) TextTexture(fontName string, color color.Color, text string) (Texture, error) {
+	font := f.Font(fontName)
+	if font == nil {
+		return nil, fmt.Errorf("no font with name '%s'", fontName)
+	}
+	return f.render.TextTexture(font, color, text)
+}
diff --git a/ui/renderer.go b/ui/renderer.go
index 85a2488..570b07f 100644
--- a/ui/renderer.go
+++ b/ui/renderer.go
@@ -5,6 +5,7 @@ import (
 	"image/color"
 
 	"opslag.de/schobers/geom"
+	"opslag.de/schobers/zntg"
 )
 
 type Renderer interface {
@@ -36,8 +37,24 @@ type Renderer interface {
 	Target() Texture
 	Text(font Font, p geom.PointF32, color color.Color, text string)
 	TextAlign(font Font, p geom.PointF32, color color.Color, text string, align HorizontalAlignment)
+	TextTexture(font Font, color color.Color, text string) (Texture, error)
 
 	// Resources
 	Resources() Resources
 	SetResourceProvider(factory func() Resources)
 }
+
+// TextTexture renders specified text to a new texture.
+func TextTexture(render Renderer, font Font, color color.Color, text string) (Texture, error) {
+	target := render.Target()
+	defer render.RenderTo(target)
+	bounds := font.Measure(text)
+	texture, err := render.CreateTextureTarget(bounds.Dx(), bounds.Dy())
+	if err != nil {
+		return nil, err
+	}
+	render.RenderTo(texture)
+	render.Clear(zntg.MustHexColor(`#00000000`))
+	render.Text(font, bounds.Min.Invert(), color, text)
+	return texture, nil
+}