Fix OpenGL, OpenGL ES, and OpenGL3 RTT textures clearing to opaque black instead of transparent

Author: Altren

ChangeLog.md

@@ -10,6 +10,7 @@
 - OpenGL: use glad for OpenGL and OpenGL3 platforms on Windows
 - OpenGL: Do not call glViewport in Platform code, as this is user responsibility
 - Fix GL3 tools/demos on macOS
+- Fix OpenGL, OpenGL ES, and OpenGL3 RTT textures clearing to opaque black instead of transparent
 
 ### Tools
 - FontConverter: new headless CLI tool that converts a ResourceTrueTypeFont XML into a ResourceManualFont XML + PNG atlas

Platforms/OpenGL3Platform/src/MyGUI_OpenGL3RTTexture.cpp

@@ -76,6 +76,7 @@ namespace MyGUI
 		glViewport(0, 0, mWidth, mHeight);
 
 		OpenGL3RenderManager::getInstance().begin();
+		glClearColor(0, 0, 0, 0);
 		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 	}
 

Platforms/OpenGLESPlatform/src/MyGUI_OpenGLESRTTexture.cpp

@@ -89,6 +89,8 @@ namespace MyGUI
 
 		OpenGLESRenderManager::getInstance().begin();
 		CHECK_GL_ERROR_DEBUG();
+		glClearColor(0, 0, 0, 0);
+		CHECK_GL_ERROR_DEBUG();
 		glClear(GL_COLOR_BUFFER_BIT /* | GL_DEPTH_BUFFER_BIT*/);
 		CHECK_GL_ERROR_DEBUG();
 	}

Platforms/OpenGLPlatform/src/MyGUI_OpenGLRTTexture.cpp

@@ -77,6 +77,7 @@ namespace MyGUI
 
 		OpenGLRenderManager::getInstance().begin();
 		glOrtho(-1, 1, 1, -1, -1, 1);
+		glClearColor(0, 0, 0, 0);
 		glClear(GL_COLOR_BUFFER_BIT /* | GL_DEPTH_BUFFER_BIT*/);
 	}