evas: fix evas flushing its command queue to wrong gl context in gl-backends

For native surface rendering (glX, egl) in gl-backend,  if pixel get callback
function is called for native rendering, there is a case where evas will
try to call evas_gl_common_context_flush() to flush its remaining commands
in its command queue while the context is set current to the native surface/
context that is called within the pixel get callback.  So, I've added an
engine function that forces a flush before it enters the pixel get callback
function.

src/lib/evas/canvas/evas_object_image.c

@@ -3812,6 +3812,9 @@ evas_object_image_render(Evas_Object *eo_obj, Evas_Object_Protected_Data *obj, v
           {
              if (o->pixels->func.get_pixels)
                {
+                  if (obj->layer->evas->engine.func->context_flush)
+                     obj->layer->evas->engine.func->context_flush(output);
+
                   // Set img object for direct rendering optimization
                   // Check for image w/h against image geometry w/h
                   // Check for image color r,g,b,a = {255,255,255,255}

src/lib/evas/include/evas_private.h

@@ -896,6 +896,8 @@ struct _Evas_Func
    Eina_Bool (*multi_font_draw)          (void *data, void *context, void *surface, Evas_Font_Set *font, int x, int y, int w, int h, int ow, int oh, Evas_Font_Array *texts, Eina_Bool do_async);
 
    Eina_Bool (*pixel_alpha_get)          (void *image, int x, int y, DATA8 *alpha, int src_region_x, int src_region_y, int src_region_w, int src_region_h, int dst_region_x, int dst_region_y, int dst_region_w, int dst_region_h);
+
+   void (*context_flush)                 (void *data);
 };
 
 struct _Evas_Image_Save_Func

src/modules/evas/engines/gl_x11/evas_engine.c

@@ -3270,6 +3270,16 @@ eng_pixel_alpha_get(void *image, int x, int y, DATA8 *alpha, int src_region_x, i
    return EINA_TRUE;
 }
 
+static void
+eng_context_flush(void *data)
+{
+   Render_Engine *re;
+   re = (Render_Engine *)data;
+
+   eng_window_use(re->win);
+   evas_gl_common_context_flush(re->win->gl_context);
+}
+
 static int
 module_open(Evas_Module *em)
 {
@@ -3388,6 +3398,8 @@ module_open(Evas_Module *em)
 
    ORD(pixel_alpha_get);
 
+   ORD(context_flush);
+
    /* now advertise out own api */
    em->functions = (void *)(&func);
    return 1;

src/modules/evas/engines/software_generic/evas_engine.c

@@ -2674,6 +2674,7 @@ static Evas_Func func =
      NULL,
      eng_multi_font_draw,
      eng_pixel_alpha_get,
+     NULL, // eng_context_flush - software doesn't use it
    /* FUTURE software generic calls go here */
 };
 

src/modules/evas/engines/wayland_egl/evas_engine.c

@@ -3691,6 +3691,16 @@ eng_image_max_size_get(void *data, int *maxw, int *maxh)
    if (maxh) *maxh = re->win->gl_context->shared->info.max_texture_size;
 }
 
+static void
+eng_context_flush(void *data)
+{
+   Render_Engine *re;
+   re = (Render_Engine *)data;
+
+   eng_window_use(re->win);
+   evas_gl_common_context_flush(re->win->gl_context);
+}
+
 static int
 module_open(Evas_Module *em)
 {
@@ -3807,6 +3817,8 @@ module_open(Evas_Module *em)
 
    ORD(image_max_size_get);
 
+   ORD(context_flush);
+
    /* now advertise out own api */
    em->functions = (void *)(&func);
    return 1;