From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 15 Jul 2015 20:36:54 +0000 (+0300)
Subject: Add a class for easier text rendering
X-Git-Url: http://git.tdb.fi/?a=commitdiff_plain;h=31e788548ca4875539ad59c4fbec26ab90517141;p=libs%2Fgl.git

Add a class for easier text rendering

I've written the equivalent in various applications a few times, so might
as well put it here.
---

diff --git a/source/text.cpp b/source/text.cpp
new file mode 100644
index 00000000..e3a85400
--- /dev/null
+++ b/source/text.cpp
@@ -0,0 +1,95 @@
+#include "meshbuilder.h"
+#include "text.h"
+#include "texture2d.h"
+
+using namespace std;
+
+namespace Msp {
+namespace GL {
+
+Text::Text(const Font &f, const Technique *tech):
+	font(f),
+	mesh((TEXCOORD2, VERTEX2)),
+	horz_align(0.0f),
+	vert_offset(0.0f)
+{
+	object.set_mesh(&mesh);
+	if(tech)
+		set_technique(tech);
+}
+
+void Text::set_technique(const Technique *tech)
+{
+	if(tech)
+	{
+		technique = *tech;
+		technique.replace_texture("diffusemap", font.get_texture());
+		object.set_technique(&technique);
+	}
+	else
+		object.set_technique(0);
+}
+
+void Text::set_text(const string &text, StringCodec::Decoder &dec)
+{
+	clear();
+	width = font.get_string_width(text, dec);
+	GL::MeshBuilder bld(mesh);
+	bld.matrix() *= Matrix::translation(Vector3(-horz_align*width, vert_offset, 0.0f));
+	font.build_string(text, dec, bld);
+}
+
+void Text::clear()
+{
+	mesh.clear();
+	width = 0;
+}
+
+void Text::set_alignment(HorizontalAlign ha, VerticalAlign va)
+{
+	float h;
+	switch(ha)
+	{
+	case LEFT: h = 0.0f; break;
+	case CENTER: h = 0.5f; break;
+	case RIGHT: h = 1.0f; break;
+	default: throw invalid_argument("Text::set_alignment");
+	}
+
+	float v;
+	switch(va)
+	{
+	case DESCENT: v = -font.get_descent(); break;
+	case BASELINE: v = 0.0f; break;
+	case MIDLINE: v = font.get_ascent()/2; break;  // XXX Midline should be cap height / 2
+	case ASCENT: v = font.get_ascent(); break;
+	default: throw invalid_argument("Text::set_alignment");
+	}
+
+	set_alignment(h, v);
+}
+
+void Text::set_alignment(float h, float v)
+{
+	float horz_adjust = (horz_align-h)*width;
+	float vert_adjust = -v-vert_offset;
+	horz_align = h;
+	vert_offset = -v;
+
+	unsigned pos_offset = mesh.get_vertices().get_format().offset(VERTEX2);
+	unsigned n_vertices = mesh.get_n_vertices();
+	for(unsigned i=0; i<n_vertices; ++i)
+	{
+		float *pos = mesh.modify_vertex(i)+pos_offset;
+		pos[0] += horz_adjust;
+		pos[1] += vert_adjust;
+	}
+}
+
+void Text::render(Renderer &renderer, const Tag &tag) const
+{
+	object.render(renderer, tag);
+}
+
+} // namespace GL
+} // namespace Msp
diff --git a/source/text.h b/source/text.h
new file mode 100644
index 00000000..ab1bfe93
--- /dev/null
+++ b/source/text.h
@@ -0,0 +1,87 @@
+#ifndef MSP_GL_TEXT_H_
+#define MSP_GL_TEXT_H_
+
+#include "font.h"
+#include "mesh.h"
+#include "object.h"
+#include "technique.h"
+
+namespace Msp {
+namespace GL {
+
+/**
+Creates an object consisting of the visual representation of a string.  Can be
+used with an ObjectInstance to further customize the appearance.
+*/
+class Text: public Renderable
+{
+public:
+	enum HorizontalAlign
+	{
+		LEFT,
+		CENTER,
+		RIGHT
+	};
+
+	enum VerticalAlign
+	{
+		DESCENT,
+		BASELINE,
+		MIDLINE,
+		ASCENT
+	};
+
+private:
+	const Font &font;
+	Mesh mesh;
+	Object object;
+	Technique technique;
+	float horz_align;
+	float vert_offset;
+	float width;
+
+public:
+	Text(const Font &, const Technique * = 0);
+
+	const Mesh *get_mesh() const { return &mesh; }
+
+	/** Sets technique to render with.  It should have a texture slot named
+	"diffusemap", which will be replaced with the font's texture. */
+	void set_technique(const Technique *);
+
+	const Technique *get_technique() const { return object.get_technique(); }
+
+	/// Sets the string to be displayed.
+	void set_text(const std::string &, StringCodec::Decoder &);
+
+	template<typename C>
+	void set_text(const std::string &t)
+	{
+		typename C::Decoder dec;
+		set_text(t, dec);
+	}
+
+	void set_text(const std::string &t)
+	{ set_text<StringCodec::Utf8>(t); }
+
+	/// Clears the object's contents.
+	void clear();
+
+	/// Sets horizontal and vertical alignment with predefined anchors.
+	void set_alignment(HorizontalAlign, VerticalAlign = BASELINE);
+
+	/** Sets horizontal and vertical alignment.  0.0 means left or baseline,
+	1.0 means right or top. */
+	void set_alignment(float, float = 0.0f);
+
+	float get_width() const { return width; }
+
+	virtual void render(Renderer &, const Tag &) const;
+
+	operator const Object &() const { return object; }
+};
+
+} // namespace GL
+} // namespace Msp
+
+#endif