From 5406a689595b5e33aab55840210669b5062989cf Mon Sep 17 00:00:00 2001
From: janwas <jan@wildfiregames.com>
Date: Sat, 20 Aug 2011 17:56:12 +0000
Subject: [PATCH] feature request by philip: instead of refusing to load
 textures larger than the OpenGL limit, ensure they have mipmaps (unless it's
 s3tc, which would be too expensive to recompress) and skip levels until it
 fits

This was SVN commit r10043.
---
 source/lib/res/graphics/ogl_tex.cpp | 30 +++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/source/lib/res/graphics/ogl_tex.cpp b/source/lib/res/graphics/ogl_tex.cpp
index 57ee36e1a7..f8fc9f1433 100644
--- a/source/lib/res/graphics/ogl_tex.cpp
+++ b/source/lib/res/graphics/ogl_tex.cpp
@@ -77,8 +77,13 @@ static bool wrap_valid(GLint wrap)
 }
 
 
-static bool filter_uses_mipmaps(GLint filter)
+static bool are_mipmaps_needed(size_t width, size_t height, GLint filter)
 {
+	// can't upload the entire texture; we're going to skip some
+	// levels until it no longer exceeds the OpenGL dimension limit.
+	if((GLint)width > ogl_max_tex_size || (GLint)height > ogl_max_tex_size)
+		return true;
+
 	switch(filter)
 	{
 	case GL_NEAREST_MIPMAP_NEAREST:
@@ -466,16 +471,15 @@ static Status OglTex_validate(const OglTex* ot)
 		// .. == 0; texture file probably not loaded successfully.
 		if(w == 0 || h == 0)
 			WARN_RETURN(ERR::_11);
-		// .. greater than max supported tex dimension.
-		//    no-op if ogl_Init not yet called
-		if(w > (size_t)ogl_max_tex_size || h > (size_t)ogl_max_tex_size)
-			WARN_RETURN(ERR::_12);
 		// .. not power-of-2.
 		//    note: we can't work around this because both NV_texture_rectangle
 		//    and subtexture require work for the client (changing tex coords).
 		//    TODO: ARB_texture_non_power_of_two
 		if(!is_pow2(w) || !is_pow2(h))
 			WARN_RETURN(ERR::_13);
+
+		// no longer verify dimensions are less than ogl_max_tex_size,
+		// because we just use the higher mip levels in that case.
 	}
 
 	// texture state
@@ -754,7 +758,7 @@ static Status get_mipmaps(Tex* t, GLint filter, int q_flags, int* plevels_to_ski
 {
 	// decisions:
 	// .. does filter call for uploading mipmaps?
-	const bool need_mipmaps = filter_uses_mipmaps(filter);
+	const bool need_mipmaps = are_mipmaps_needed(t->w, t->h, filter);
 	// .. does the image data include mipmaps? (stored as separate
 	//    images after the regular texels)
 	const bool includes_mipmaps = (t->flags & TEX_MIPMAPS) != 0;
@@ -798,14 +802,24 @@ static Status get_mipmaps(Tex* t, GLint filter, int q_flags, int* plevels_to_ski
 	// t contains mipmaps; we can apply our resolution reduction trick:
 	if(*plevels_to_skip == 0)
 	{
+		// if OpenGL's texture dimension limit is too small, use the
+		// higher mipmap levels. NB: the minimum guaranteed size is
+		// far too low, and menu background textures may be large.
+		GLint w = (GLint)t->w, h = (GLint)t->h;
+		while(w > ogl_max_tex_size || h > ogl_max_tex_size)
+		{
+			(*plevels_to_skip)++;
+			w /= 2; h /= 2;	// doesn't matter if either dimension drops to 0
+		}
+
 		// this saves texture memory by skipping some of the lower
 		// (high-resolution) mip levels.
 		//
 		// note: we don't just use GL_TEXTURE_BASE_LEVEL because it would
 		// require uploading unused levels, which is wasteful.
 		// .. can be expanded to reduce to 1/4, 1/8 by encoding factor in q_flags.
-		const size_t reduce = (q_flags & OGL_TEX_HALF_RES)? 2 : 1;
-		*plevels_to_skip = (int)ceil_log2(reduce);
+		if(q_flags & OGL_TEX_HALF_RES)
+			(*plevels_to_skip)++;
 	}
 
 	return INFO::OK;