[gtk/offscreen-fixes: 3/5] ngl: Fix offscreen rendering with transforms

[Matthias Clasen <matthiasc src gnome org>]

commit f9457af128012fd3935a69fdcefb722df3ad189c
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Mar 31 14:36:24 2021 -0400

    ngl: Fix offscreen rendering with transforms
    
    There was confusion here about the handling of the
    modelview transform. The modelview transform we are
    getting is already set up for rendering the node
    we are given, so keep it - except for possible adding
    an extra scale on top when the texture would otherwise
    be too big.

 gsk/ngl/gsknglrenderjob.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)
---
diff --git a/gsk/ngl/gsknglrenderjob.c b/gsk/ngl/gsknglrenderjob.c
index 08e99a7d19..1e62b4ecc7 100644
--- a/gsk/ngl/gsknglrenderjob.c
+++ b/gsk/ngl/gsknglrenderjob.c
@@ -3566,8 +3566,8 @@ gsk_ngl_render_job_visit_node_with_offscreen (GskNglRenderJob       *job,
 
   float scaled_width;
   float scaled_height;
-  float scale_x = job->scale_x;
-  float scale_y = job->scale_y;
+  float downscale_x = 1;
+  float downscale_y = 1;
 
   g_assert (job->command_queue->max_texture_size > 0);
 
@@ -3578,17 +3578,17 @@ gsk_ngl_render_job_visit_node_with_offscreen (GskNglRenderJob       *job,
   {
     int max_texture_size = job->command_queue->max_texture_size;
 
-    scaled_width = ceilf (offscreen->bounds->size.width * scale_x);
+    scaled_width = ceilf (offscreen->bounds->size.width * job->scale_x);
     if (scaled_width > max_texture_size)
       {
-        scale_x *= (float)max_texture_size / scaled_width;
+        downscale_x = (float)max_texture_size / scaled_width;
         scaled_width = max_texture_size;
       }
 
-    scaled_height = ceilf (offscreen->bounds->size.height * scale_y);
+    scaled_height = ceilf (offscreen->bounds->size.height * job->scale_y);
     if (scaled_height > max_texture_size)
       {
-        scale_y *= (float)max_texture_size / scaled_height;
+        downscale_y = (float)max_texture_size / scaled_height;
         scaled_height = max_texture_size;
       }
   }
@@ -3632,10 +3632,9 @@ gsk_ngl_render_job_visit_node_with_offscreen (GskNglRenderJob       *job,
 
   gsk_ngl_render_job_set_viewport (job, &viewport, &prev_viewport);
   gsk_ngl_render_job_set_projection_from_rect (job, &job->viewport, &prev_projection);
-  gsk_ngl_render_job_set_modelview (job, gsk_transform_scale (NULL, scale_x, scale_y));
+  if (downscale_x != 1 || downscale_y != 1)
+    gsk_ngl_render_job_push_modelview (job, gsk_transform_scale (NULL, downscale_x, downscale_y));
   prev_alpha = gsk_ngl_render_job_set_alpha (job, 1.0f);
-  job->offset_x = offset_x;
-  job->offset_y = offset_y;
 
   prev_fbo = gsk_ngl_command_queue_bind_framebuffer (job->command_queue, render_target->framebuffer_id);
   gsk_ngl_command_queue_clear (job->command_queue, 0, &job->viewport);
@@ -3648,7 +3647,8 @@ gsk_ngl_render_job_visit_node_with_offscreen (GskNglRenderJob       *job,
   if (offscreen->reset_clip)
     gsk_ngl_render_job_pop_clip (job);
 
-  gsk_ngl_render_job_pop_modelview (job);
+  if (downscale_x != 1 || downscale_y != 1)
+    gsk_ngl_render_job_pop_modelview (job);
   gsk_ngl_render_job_set_viewport (job, &prev_viewport, NULL);
   gsk_ngl_render_job_set_projection (job, &prev_projection);
   gsk_ngl_render_job_set_alpha (job, prev_alpha);