Extract OpenGL filter wrapper

In order to implement several standalone video filters (with capability
"video filter") using OpenGL filters (with capability "opengl filter"),
define an helper to delegate the work to the "opengl" video filter.

Co-authored-by: vatsin1810 <suchak@sas.upenn.edu>

modules/video_filter/deinterlace/glblend.c

@@ -205,16 +205,7 @@ static int OpenVideoFilter(vlc_object_t *obj)
     if (!is_supported)
         return VLC_EGENERIC;
 
-    const config_chain_t *prev_chain = filter->p_cfg;
-    var_Create(filter, "opengl-filter", VLC_VAR_STRING);
-    var_SetString(filter, "opengl-filter", "glblend");
-
-    filter->p_cfg = NULL;
-    module_t *module = module_need(obj, "video filter", "opengl", true);
-    filter->p_cfg = prev_chain;
-
-    var_Destroy(filter, "opengl-filter");
-
+    module_t *module = vlc_gl_WrapOpenGLFilter(filter, "glblend");
     if (module == NULL)
         return VLC_EGENERIC;
 

modules/video_output/opengl/gl_util.c

@@ -25,6 +25,9 @@
 
 #include "gl_util.h"
 
+#include <vlc_filter.h>
+#include <vlc_modules.h>
+
 static void
 LogShaderErrors(vlc_object_t *obj, const opengl_vtable_t *vt, GLuint id)
 {
@@ -131,3 +134,19 @@ finally_1:
 
     return program;
 }
+
+module_t *
+vlc_gl_WrapOpenGLFilter(filter_t *filter, const char *opengl_filter_name)
+{
+    const config_chain_t *prev_chain = filter->p_cfg;
+    var_Create(filter, "opengl-filter", VLC_VAR_STRING);
+    var_SetString(filter, "opengl-filter", opengl_filter_name);
+
+    filter->p_cfg = NULL;
+    module_t *module = module_need(filter, "video filter", "opengl", true);
+    filter->p_cfg = prev_chain;
+
+    var_Destroy(filter, "opengl-filter");
+
+    return module;
+}

modules/video_output/opengl/gl_util.h

@@ -70,4 +70,16 @@ vlc_gl_BuildProgram(vlc_object_t *obj, const opengl_vtable_t *vt,
                     GLsizei vstring_count, const GLchar **vstrings,
                     GLsizei fstring_count, const GLchar **fstrings);
 
+/**
+ * Wrap an OpenGL filter from a video filter
+ *
+ * Open an OpenGL filter (with capability "opengl filter") from a video filter
+ * (with capability "video filter").
+ *
+ * This internally uses the "opengl" video filter to load the OpenGL filter
+ * with the given name.
+ */
+module_t *
+vlc_gl_WrapOpenGLFilter(filter_t *filter, const char *opengl_filter_name);
+
 #endif