From 59ac6d3971dcec30fcbe5283fc3cdb45e5d27dcf Mon Sep 17 00:00:00 2001
From: Ruslan Kabatsayev <b7.10110111@gmail.com>
Date: Fri, 7 Apr 2023 00:47:37 +0400
Subject: [PATCH] Generate mipmap pyramid manually for GL_RGB textures if
 glGenerateMipmap() fails

This failure can happen in GLES2 mode when GL_SRGB8 is not color renderable.
---
 src/core/StelTexture.cpp | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/src/core/StelTexture.cpp b/src/core/StelTexture.cpp
index 8a5085411b874..a7b940543f592 100644
--- a/src/core/StelTexture.cpp
+++ b/src/core/StelTexture.cpp
@@ -432,7 +432,25 @@ bool StelTexture::glLoad(const GLData& data)
 		{
 			glSize = glSize + glSize/3; //mipmaps require 1/3 more mem
 		}
+
+		StelOpenGL::checkGLErrors(__FILE__, __LINE__);
 		gl->glGenerateMipmap(GL_TEXTURE_2D);
+
+		const bool manualMipmapGeneration = gl->glGetError() != GL_NO_ERROR;
+		if(manualMipmapGeneration && data.format==GL_RGB)
+		{
+			// Formula from the glspec, "Mipmapping" subsection in section 3.8.11 Texture Minification
+			const int totalMipmapLevels = 1+std::floor(std::log2(std::max(width,height)));
+			qDebug().nospace() << "Making a mipmap pyramid for a " << width << "×" << height << " RGB texture";
+			QImage img(reinterpret_cast<const uchar*>(data.data.constData()), width, height, QImage::Format_RGB888);
+			for(int level=1; level<totalMipmapLevels; ++level)
+			{
+				img = img.scaled(std::max(1, img.width()/2), std::max(1, img.height()/2),
+								 Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
+				gl->glTexImage2D(GL_TEXTURE_2D, level, internalFormat, img.width(), img.height(), 0,
+								 static_cast<GLenum>(data.format), static_cast<GLenum>(data.type), img.bits());
+			}
+		}
 	}
 
 	//register ID with textureMgr and increment size