Clean anim buffer

clean_anim_buffer.patch

From 373b1b9c470e25cab99622947c7d999002a411bf Mon Sep 17 00:00:00 2001
From: Michael Lutz <michi@icosahedron.de>
Date: Fri, 19 Mar 2021 23:55:54 +0100
Subject: Fix: [OpenGL] Clear animation buffer upon creation.

---
 src/video/opengl.cpp | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/video/opengl.cpp b/src/video/opengl.cpp
index 26f6f4b4d..266434f83 100644
--- a/src/video/opengl.cpp
+++ b/src/video/opengl.cpp
@@ -944,8 +944,19 @@ bool OpenGLBackend::Resize(int w, int h, bool force)
 			_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->anim_pbo);
 			_glBufferData(GL_PIXEL_UNPACK_BUFFER, pitch * h, nullptr, GL_DYNAMIC_DRAW);
 		}
-		_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
 
+		if (_glClearBufferSubData != nullptr) {
+			byte b = 0;
+			_glClearBufferSubData(GL_PIXEL_UNPACK_BUFFER, GL_R8, 0, pitch * h, GL_RED, GL_UNSIGNED_BYTE, &b);
+		} else {
+			byte *buf = (byte *)_glMapBuffer(GL_PIXEL_UNPACK_BUFFER, GL_READ_WRITE);
+			for (int i = 0; i < pitch * h; i++) {
+				*buf++ = 0;
+			}
+			_glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER);
+		}
+
+		_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
 		_glBindTexture(GL_TEXTURE_2D, this->anim_texture);
 		_glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, w, h, 0, GL_RED, GL_UNSIGNED_BYTE, nullptr);
 	} else {
-- 
2.21.0