[gtk/layout-manager-transform-demo: 10/14] gl: Use GL_LINEAR for some offscreen rendering

[Matthias Clasen <matthiasc src gnome org>]

commit ca8a0bd1f4f288e11e72f92d30b39148446e29f2
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Sep 2 18:01:06 2020 -0400

    gl: Use GL_LINEAR for some offscreen rendering
    
    When we are dealing with full 3D transforms,
    use GL_LINEAR for interpolation, since that provides
    better rendering. We still use GL_NEAREST for pixel
    perfect results when the transforms are 2D.

 gsk/gl/gskgldriver.c        |  4 +++-
 gsk/gl/gskgldriverprivate.h |  2 ++
 gsk/gl/gskglrenderer.c      | 23 ++++++++++++++++++++---
 3 files changed, 25 insertions(+), 4 deletions(-)
---
diff --git a/gsk/gl/gskgldriver.c b/gsk/gl/gskgldriver.c
index 8cd32d72ab..08e19a980f 100644
--- a/gsk/gl/gskgldriver.c
+++ b/gsk/gl/gskgldriver.c
@@ -594,6 +594,8 @@ void
 gsk_gl_driver_create_render_target (GskGLDriver *self,
                                     int          width,
                                     int          height,
+                                    int          min_filter,
+                                    int          mag_filter,
                                     int         *out_texture_id,
                                     int         *out_render_target_id)
 {
@@ -604,7 +606,7 @@ gsk_gl_driver_create_render_target (GskGLDriver *self,
 
   texture = create_texture (self, width, height);
   gsk_gl_driver_bind_source_texture (self, texture->texture_id);
-  gsk_gl_driver_init_texture_empty (self, texture->texture_id, GL_NEAREST, GL_NEAREST);
+  gsk_gl_driver_init_texture_empty (self, texture->texture_id, min_filter, mag_filter);
 
   glGenFramebuffers (1, &fbo_id);
   glBindFramebuffer (GL_FRAMEBUFFER, fbo_id);
diff --git a/gsk/gl/gskgldriverprivate.h b/gsk/gl/gskgldriverprivate.h
index 83d0c46af9..22c5ef8cb3 100644
--- a/gsk/gl/gskgldriverprivate.h
+++ b/gsk/gl/gskgldriverprivate.h
@@ -45,6 +45,8 @@ int             gsk_gl_driver_create_texture            (GskGLDriver     *driver
 void            gsk_gl_driver_create_render_target      (GskGLDriver     *driver,
                                                          int              width,
                                                          int              height,
+                                                         int              min_filter,
+                                                         int              mag_filter,
                                                          int             *out_texture_id,
                                                          int             *out_render_target_id);
 void            gsk_gl_driver_mark_texture_permanent    (GskGLDriver     *self,
diff --git a/gsk/gl/gskglrenderer.c b/gsk/gl/gskglrenderer.c
index 5078aeef65..712939e0a4 100644
--- a/gsk/gl/gskglrenderer.c
+++ b/gsk/gl/gskglrenderer.c
@@ -71,6 +71,7 @@ typedef enum
   RESET_OPACITY    = 1 << 2,
   DUMP_FRAMEBUFFER = 1 << 3,
   NO_CACHE_PLZ     = 1 << 5,
+  LINEAR_FILTER    = 1 << 6,
 } OffscreenFlags;
 
 static inline void
@@ -1054,7 +1055,7 @@ render_transform_node (GskGLRenderer   *self,
                                    &child->bounds,
                                    child,
                                    &region, &is_offscreen,
-                                   RESET_CLIP | RESET_OPACITY))
+                                   RESET_CLIP | RESET_OPACITY | LINEAR_FILTER))
           {
             /* For non-trivial transforms, we draw everything on a texture and then
              * draw the texture transformed. */
@@ -1451,10 +1452,12 @@ blur_texture (GskGLRenderer       *self,
 
   gsk_gl_driver_create_render_target (self->gl_driver,
                                       texture_to_blur_width, texture_to_blur_height,
+                                      GL_NEAREST, GL_NEAREST,
                                       &pass1_texture_id, &pass1_render_target);
 
   gsk_gl_driver_create_render_target (self->gl_driver,
                                       texture_to_blur_width, texture_to_blur_height,
+                                      GL_NEAREST, GL_NEAREST,
                                       &pass2_texture_id, &pass2_render_target);
 
   graphene_matrix_init_ortho (&item_proj,
@@ -1696,6 +1699,7 @@ render_inset_shadow_node (GskGLRenderer   *self,
 
       gsk_gl_driver_create_render_target (self->gl_driver,
                                           texture_width, texture_height,
+                                          GL_NEAREST, GL_NEAREST,
                                           &texture_id, &render_target);
 
       graphene_matrix_init_ortho (&item_proj,
@@ -1869,7 +1873,9 @@ render_outset_shadow_node (GskGLRenderer   *self,
       graphene_rect_t prev_viewport;
       graphene_matrix_t item_proj;
 
-      gsk_gl_driver_create_render_target (self->gl_driver, texture_width, texture_height,
+      gsk_gl_driver_create_render_target (self->gl_driver,
+                                          texture_width, texture_height,
+                                          GL_NEAREST, GL_NEAREST,
                                           &texture_id, &render_target);
       if (gdk_gl_context_has_debug (self->gl_context))
         {
@@ -3349,6 +3355,7 @@ add_offscreen_ops (GskGLRenderer         *self,
   float prev_opacity = 1.0;
   int texture_id = 0;
   int max_texture_size;
+  int filter;
 
   if (node_is_invisible (child_node))
     {
@@ -3401,7 +3408,17 @@ add_offscreen_ops (GskGLRenderer         *self,
   width  = ceilf (width * scale);
   height = ceilf (height * scale);
 
-  gsk_gl_driver_create_render_target (self->gl_driver, width, height, &texture_id, &render_target);
+  if (flags & LINEAR_FILTER)
+    {
+      filter = GL_LINEAR;
+      g_print ("using GL_LINEAR for offscreen rendering\n");
+    }
+  else
+    filter = GL_NEAREST;
+  gsk_gl_driver_create_render_target (self->gl_driver,
+                                      width, height,
+                                      filter, filter,
+                                      &texture_id, &render_target);
   if (gdk_gl_context_has_debug (self->gl_context))
     {
       gdk_gl_context_label_object_printf (self->gl_context, GL_TEXTURE, texture_id,