Fix uninitialized data in render buffers at creation

src/gl/renderer/gl_renderbuffers.cpp

@@ -336,6 +336,7 @@ GLuint FGLRenderBuffers::CreateFrameBuffer(GLuint colorbuffer)
 	glBindFramebuffer(GL_FRAMEBUFFER, handle);
 	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, colorbuffer, 0);
 	CheckFrameBufferCompleteness();
+	ClearFrameBuffer();
 	return handle;
 }
 
@@ -350,6 +351,7 @@ GLuint FGLRenderBuffers::CreateFrameBuffer(GLuint colorbuffer, GLuint depthstenc
 		glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, colorbuffer, 0);
 	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, depthstencil);
 	CheckFrameBufferCompleteness();
+	ClearFrameBuffer();
 	return handle;
 }
 
@@ -365,6 +367,7 @@ GLuint FGLRenderBuffers::CreateFrameBuffer(GLuint colorbuffer, GLuint depth, GLu
 	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depth);
 	glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_RENDERBUFFER, stencil);
 	CheckFrameBufferCompleteness();
+	ClearFrameBuffer();
 	return handle;
 }
 
@@ -396,6 +399,30 @@ void FGLRenderBuffers::CheckFrameBufferCompleteness()
 	I_FatalError(error);
 }
 
+//==========================================================================
+//
+// Clear frame buffer to make sure it never contains uninitialized data
+//
+//==========================================================================
+
+void FGLRenderBuffers::ClearFrameBuffer()
+{
+	GLint scissorEnabled, stencilValue;
+	GLdouble depthValue;
+	glGetIntegerv(GL_SCISSOR_TEST, &scissorEnabled);
+	glGetIntegerv(GL_STENCIL_CLEAR_VALUE, &stencilValue);
+	glGetDoublev(GL_DEPTH_CLEAR_VALUE, &depthValue);
+	glDisable(GL_SCISSOR_TEST);
+	glClearColor(0.0, 0.0, 0.0, 0.0);
+	glClearDepth(0.0);
+	glClearStencil(0);
+	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+	glClearStencil(stencilValue);
+	glClearDepth(depthValue);
+	if (scissorEnabled)
+		glEnable(GL_SCISSOR_TEST);
+}
+
 //==========================================================================
 //
 // Resolves the multisample frame buffer by copying it to the scene texture

src/gl/renderer/gl_renderbuffers.h

@@ -54,6 +54,7 @@ private:
 	GLuint CreateFrameBuffer(GLuint colorbuffer, GLuint depthstencil, bool colorIsARenderBuffer);
 	GLuint CreateFrameBuffer(GLuint colorbuffer, GLuint depth, GLuint stencil, bool colorIsARenderBuffer);
 	void CheckFrameBufferCompleteness();
+	void ClearFrameBuffer();
 	void DeleteTexture(GLuint &handle);
 	void DeleteRenderBuffer(GLuint &handle);
 	void DeleteFrameBuffer(GLuint &handle);