From 91169c82c7bcaff0c43ac7582bbbb7aa347c69b7 Mon Sep 17 00:00:00 2001
From: Ykkrosh <philip@wildfiregames.com>
Date: Fri, 18 Oct 2013 16:05:02 +0000
Subject: [PATCH] Optimise rendering of scrollable text boxes by clipping

Add optional clipping rectangle to CTextRenderer. Strings that are
printed
outside the vertical extent of the clipping rectangle will be
immediately
skipped. This greatly reduces the cost of large scrollable text boxes.

This was SVN commit r14019.
---
 source/graphics/Font.h           | 13 +++++++++++++
 source/graphics/FontManager.cpp  | 10 ++++++++++
 source/graphics/TextRenderer.cpp | 15 +++++++++++++++
 source/graphics/TextRenderer.h   |  9 +++++++++
 source/gui/CGUI.cpp              |  6 ++++--
 5 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/source/graphics/Font.h b/source/graphics/Font.h
index 2a44c7c128..3a739e766e 100644
--- a/source/graphics/Font.h
+++ b/source/graphics/Font.h
@@ -74,6 +74,13 @@ public:
 	int GetHeight() const { return m_Height; }
 	int GetCharacterWidth(wchar_t c) const;
 	void CalculateStringSize(const wchar_t* string, int& w, int& h) const;
+	void GetGlyphBounds(float& x0, float& y0, float& x1, float& y1) const
+	{
+		x0 = m_BoundsX0;
+		y0 = m_BoundsY0;
+		x1 = m_BoundsX1;
+		y1 = m_BoundsY1;
+	}
 	const GlyphMap& GetGlyphs() const { return m_Glyphs; }
 	CTexturePtr GetTexture() const { return m_Texture; }
 
@@ -86,6 +93,12 @@ private:
 
 	int m_LineSpacing;
 	int m_Height; // height of a capital letter, roughly
+
+	// Bounding box of all glyphs
+	float m_BoundsX0;
+	float m_BoundsY0;
+	float m_BoundsX1;
+	float m_BoundsY1;
 };
 
 #endif // INCLUDED_FONT
diff --git a/source/graphics/FontManager.cpp b/source/graphics/FontManager.cpp
index 6f9722bce6..4bffa209b8 100644
--- a/source/graphics/FontManager.cpp
+++ b/source/graphics/FontManager.cpp
@@ -88,6 +88,11 @@ bool CFontManager::ReadFont(CFont* font, const CStrW& fontName)
 	FNTStream >> font->m_LineSpacing;
 	FNTStream >> font->m_Height;
 
+	font->m_BoundsX0 = FLT_MAX;
+	font->m_BoundsY0 = FLT_MAX;
+	font->m_BoundsX1 = -FLT_MAX;
+	font->m_BoundsY1 = -FLT_MAX;
+
 	for (int i = 0; i < NumGlyphs; ++i)
 	{
 		int          Codepoint, TextureX, TextureY, Width, Height, OffsetX, OffsetY, Advance;
@@ -106,6 +111,11 @@ bool CFontManager::ReadFont(CFont* font, const CStrW& fontName)
 
 		CFont::GlyphData g = { u, -v, u+w, -v+h, (i16)OffsetX, (i16)-OffsetY, (i16)(OffsetX+Width), (i16)(-OffsetY+Height), (i16)Advance };
 		font->m_Glyphs.set((u16)Codepoint, g);
+
+		font->m_BoundsX0 = std::min(font->m_BoundsX0, (float)g.x0);
+		font->m_BoundsY0 = std::min(font->m_BoundsY0, (float)g.y0);
+		font->m_BoundsX1 = std::max(font->m_BoundsX1, (float)g.x1);
+		font->m_BoundsY1 = std::max(font->m_BoundsY1, (float)g.y1);
 	}
 
 	ENSURE(font->m_Height); // Ensure the height has been found (which should always happen if the font includes an 'I')
diff --git a/source/graphics/TextRenderer.cpp b/source/graphics/TextRenderer.cpp
index 01a6320400..c150cf81ae 100644
--- a/source/graphics/TextRenderer.cpp
+++ b/source/graphics/TextRenderer.cpp
@@ -66,6 +66,11 @@ void CTextRenderer::Translate(float x, float y, float z)
 	m_Dirty = true;
 }
 
+void CTextRenderer::SetClippingRect(const CRect& rect)
+{
+	m_Clipping = rect;
+}
+
 void CTextRenderer::Color(const CColor& color)
 {
 	if (m_Color != color)
@@ -151,6 +156,16 @@ void CTextRenderer::PutString(float x, float y, const std::wstring* buf, bool ow
 	if (!m_Font)
 		return; // invalid font; can't render
 
+	if (m_Clipping != CRect())
+	{
+		float x0, y0, x1, y1;
+		m_Font->GetGlyphBounds(x0, y0, x1, y1);
+		if (y + y1 < m_Clipping.top)
+			return;
+		if (y + y0 > m_Clipping.bottom)
+			return;
+	}
+
 	// If any state has changed since the last batch, start a new batch
 	if (m_Dirty)
 	{
diff --git a/source/graphics/TextRenderer.h b/source/graphics/TextRenderer.h
index de6276986d..199fe206a0 100644
--- a/source/graphics/TextRenderer.h
+++ b/source/graphics/TextRenderer.h
@@ -41,6 +41,14 @@ public:
 
 	void Translate(float x, float y, float z);
 
+	/**
+	 * Set clipping rectangle, in pre-transform coordinates (i.e. text is clipped against
+	 * this rect based purely on the x,y values passed into Put()). Text fully outside the
+	 * clipping rectangle may not be rendered. Should be used in conjunction with glScissor
+	 * for precise clipping - this is just an optimisation.
+	 */
+	void SetClippingRect(const CRect& rect);
+
 	/**
 	 * Set the color for subsequent print calls.
 	 */
@@ -149,6 +157,7 @@ private:
 	CShaderProgramPtr m_Shader;
 
 	CMatrix3D m_Transform;
+	CRect m_Clipping;
 
 	CColor m_Color;
 	CStrW m_FontName;
diff --git a/source/gui/CGUI.cpp b/source/gui/CGUI.cpp
index 59f818a4f3..0781873735 100644
--- a/source/gui/CGUI.cpp
+++ b/source/gui/CGUI.cpp
@@ -945,13 +945,15 @@ void CGUI::DrawText(SGUIText &Text, const CColor &DefaultColor,
 
 	tech->BeginPass();
 
-	if (clipping != CRect())
+	bool isClipped = (clipping != CRect());
+	if (isClipped)
 	{
 		glEnable(GL_SCISSOR_TEST);
 		glScissor(clipping.left, g_yres - clipping.bottom, clipping.GetWidth(), clipping.GetHeight());
 	}
 
 	CTextRenderer textRenderer(tech->GetShader());
+	textRenderer.SetClippingRect(clipping);
 	textRenderer.Translate(0.0f, 0.0f, z);
 
 	for (std::vector<SGUIText::STextCall>::const_iterator it = Text.m_TextCalls.begin(); 
@@ -978,7 +980,7 @@ void CGUI::DrawText(SGUIText &Text, const CColor &DefaultColor,
 		DrawSprite(it->m_Sprite, it->m_CellID, z, it->m_Area + pos);
 	}
 
-	if (clipping != CRect())
+	if (isClipped)
 		glDisable(GL_SCISSOR_TEST);
 
 	tech->EndPass();