Fix #8871: [OpenGL] Initialize all buffers after resize and clear back buffer. (#8877)

3 files changed, 38 insertions, 7 deletions

diff --git a/src/video/opengl.cpp b/src/video/opengl.cpp
index 26f6f4b4d..d142abfea 100644
--- a/src/video/opengl.cpp
+++ b/src/video/opengl.cpp
@@ -878,6 +878,22 @@ bool OpenGLBackend::InitShaders()
 }
 
 /**
+ * Clear the bound pixel buffer to a specific value.
+ * @param len Length of the buffer.
+ * @param data Value to set.
+ * @tparam T Pixel type.
+ */
+template <class T>
+static void ClearPixelBuffer(size_t len, T data)
+{
+	T *buf = reinterpret_cast<T *>(_glMapBuffer(GL_PIXEL_UNPACK_BUFFER, GL_READ_WRITE));
+	for (int i = 0; i < len; i++) {
+		*buf++ = data;
+	}
+	_glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER);
+}
+
+/**
  * Change the size of the drawing window and allocate matching resources.
  * @param w New width of the window.
  * @param h New height of the window.
@@ -911,14 +927,16 @@ bool OpenGLBackend::Resize(int w, int h, bool force)
 		if (_glClearBufferSubData != nullptr) {
 			_glClearBufferSubData(GL_PIXEL_UNPACK_BUFFER, GL_RGBA8, 0, pitch * h * bpp / 8, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, &black.data);
 		} else {
-			uint32 *buf = (uint32 *)_glMapBuffer(GL_PIXEL_UNPACK_BUFFER, GL_READ_WRITE);
-			for (int i = 0; i < pitch * h; i++) {
-				*buf++ = black.data;
-			}
-			_glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER);
+			ClearPixelBuffer<uint32>(pitch * h, black.data);
+		}
+	} else if (bpp == 8) {
+		if (_glClearBufferSubData != nullptr) {
+			byte b = 0;
+			_glClearBufferSubData(GL_PIXEL_UNPACK_BUFFER, GL_R8, 0, pitch * h, GL_RED, GL_UNSIGNED_BYTE, &b);
+		} else {
+			ClearPixelBuffer<byte>(pitch * h, 0);
 		}
 	}
-	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
 
 	_glActiveTexture(GL_TEXTURE0);
 	_glBindTexture(GL_TEXTURE_2D, this->vid_texture);
@@ -931,6 +949,7 @@ bool OpenGLBackend::Resize(int w, int h, bool force)
 			_glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, w, h, 0, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, nullptr);
 			break;
 	}
+	_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
 
 	/* Does this blitter need a separate animation buffer? */
 	if (BlitterFactory::GetCurrentBlitter()->NeedsAnimationBuffer()) {
@@ -944,10 +963,18 @@ 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);
+
+		/* Initialize buffer as 0 == no remap. */
+		if (_glClearBufferSubData != nullptr) {
+			byte b = 0;
+			_glClearBufferSubData(GL_PIXEL_UNPACK_BUFFER, GL_R8, 0, pitch * h, GL_RED, GL_UNSIGNED_BYTE, &b);
+		} else {
+			ClearPixelBuffer<byte>(pitch * h, 0);
+		}
 
 		_glBindTexture(GL_TEXTURE_2D, this->anim_texture);
 		_glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, w, h, 0, GL_RED, GL_UNSIGNED_BYTE, nullptr);
+		_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
 	} else {
 		if (this->anim_buffer != nullptr) {
 			_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->anim_pbo);
@@ -975,6 +1002,8 @@ bool OpenGLBackend::Resize(int w, int h, bool force)
 	_glUseProgram(this->remap_program);
 	_glUniform2f(this->remap_screen_loc, (float)_screen.width, (float)_screen.height);
 
+	_glClear(GL_COLOR_BUFFER_BIT);
+
 	return true;
 }
 
diff --git a/src/video/sdl2_opengl_v.cpp b/src/video/sdl2_opengl_v.cpp
index 13ee082ba..86dc104dd 100644
--- a/src/video/sdl2_opengl_v.cpp
+++ b/src/video/sdl2_opengl_v.cpp
@@ -131,6 +131,7 @@ bool VideoDriver_SDL_OpenGL::AllocateBackingStore(int w, int h, bool force)
 	MemSetT(&this->dirty_rect, 0);
 
 	bool res = OpenGLBackend::Get()->Resize(w, h, force);
+	SDL_GL_SwapWindow(this->sdl_window);
 	_screen.dst_ptr = this->GetVideoPointer();
 
 	_cur_palette.first_dirty = 0;
diff --git a/src/video/win32_v.cpp b/src/video/win32_v.cpp
index a802cdafa..1d9cd3e2b 100644
--- a/src/video/win32_v.cpp
+++ b/src/video/win32_v.cpp
@@ -1417,6 +1417,7 @@ bool VideoDriver_Win32OpenGL::AllocateBackingStore(int w, int h, bool force)
 
 	this->dirty_rect = {};
 	bool res = OpenGLBackend::Get()->Resize(w, h, force);
+	SwapBuffers(this->dc);
 	_screen.dst_ptr = this->GetVideoPointer();
 
 	return res;