libobs: Always have a transparent blank texture available

Allows transitions to be able to return a blank texture to transitions
if a transition is transitioning from/to a NULL source.

libobs/obs-internal.h

@@ -257,6 +257,8 @@ struct obs_core_video {
 	uint32_t                        base_height;
 	float                           color_matrix[16];
 	enum obs_scale_type             scale_type;
+
+	gs_texture_t                    *transparent_texture;
 };
 
 struct obs_core_audio {

libobs/obs.c

@@ -218,6 +218,8 @@ static bool obs_init_textures(struct obs_video_info *ovi)
 static int obs_init_graphics(struct obs_video_info *ovi)
 {
 	struct obs_core_video *video = &obs->video;
+	uint8_t transparent_tex_data[2*2*4] = {0};
+	const uint8_t *transparent_tex = transparent_tex_data;
 	bool success = true;
 	int errorcode;
 
@@ -278,6 +280,9 @@ static int obs_init_graphics(struct obs_video_info *ovi)
 			NULL);
 	bfree(filename);
 
+	obs->video.transparent_texture = gs_texture_create(2, 2, GS_RGBA, 1,
+			&transparent_tex, 0);
+
 	if (!video->default_effect)
 		success = false;
 	if (gs_get_device_type() == GS_DEVICE_OPENGL) {
@@ -290,6 +295,8 @@ static int obs_init_graphics(struct obs_video_info *ovi)
 		success = false;
 	if (!video->conversion_effect)
 		success = false;
+	if (!video->transparent_texture)
+		success = false;
 
 	gs_leave_context();
 	return success ? OBS_VIDEO_SUCCESS : OBS_VIDEO_FAIL;
@@ -432,6 +439,8 @@ static void obs_free_graphics(void)
 	if (video->graphics) {
 		gs_enter_context(video->graphics);
 
+		gs_texture_destroy(video->transparent_texture);
+
 		gs_effect_destroy(video->default_effect);
 		gs_effect_destroy(video->default_rect_effect);
 		gs_effect_destroy(video->opaque_effect);