mtk: Add mtk_compute_viewport_matrix helper

It'll be used to calculate a CoglPipeline layer matrix given viewport
data.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3859>

mtk/mtk/meson.build

@@ -5,6 +5,7 @@ mtk_headers = [
   'mtk-monitor-transform.h',
   'mtk-rectangle.h',
   'mtk-region.h',
+  'mtk-utils.h',
   'mtk.h',
 ]
 
@@ -12,6 +13,7 @@ mtk_sources = [
   'mtk-monitor-transform.c',
   'mtk-rectangle.c',
   'mtk-region.c',
+  'mtk-utils.c',
 ]
 
 if have_x11_client

mtk/mtk/mtk-utils.c

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2021-2024 Robert Mader <robert.mader@posteo.de>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "mtk/mtk-utils.h"
+
+void
+mtk_compute_viewport_matrix (graphene_matrix_t     *matrix,
+                             int                    width,
+                             int                    height,
+                             float                  scale,
+                             MtkMonitorTransform    transform,
+                             const graphene_rect_t *src_rect)
+{
+  if (src_rect)
+    {
+      float scaled_width;
+      float scaled_height;
+      graphene_point3d_t p;
+
+      scaled_width = width / scale;
+      scaled_height = height / scale;
+
+      graphene_point3d_init (&p,
+                             src_rect->origin.x / src_rect->size.width,
+                             src_rect->origin.y / src_rect->size.height,
+                             0);
+      graphene_matrix_translate (matrix, &p);
+
+      if (mtk_monitor_transform_is_rotated (transform))
+        {
+          graphene_matrix_scale (matrix,
+                                 src_rect->size.width / scaled_height,
+                                 src_rect->size.height / scaled_width,
+                                 1);
+        }
+      else
+        {
+          graphene_matrix_scale (matrix,
+                                 src_rect->size.width / scaled_width,
+                                 src_rect->size.height / scaled_height,
+                                 1);
+        }
+    }
+
+  mtk_monitor_transform_transform_matrix (transform, matrix);
+}

mtk/mtk/mtk-utils.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2021-2024 Robert Mader <robert.mader@posteo.de>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <graphene.h>
+
+#include "mtk/mtk-macros.h"
+#include "mtk/mtk-monitor-transform.h"
+
+MTK_EXPORT
+void mtk_compute_viewport_matrix (graphene_matrix_t     *matrix,
+                                  int                    width,
+                                  int                    height,
+                                  float                  scale,
+                                  MtkMonitorTransform    transform,
+                                  const graphene_rect_t *src_rect);

mtk/mtk/mtk.h

@@ -27,5 +27,6 @@
 #include "mtk/mtk-region.h"
 #include "mtk/mtk-macros.h"
 #include "mtk/mtk-monitor-transform.h"
+#include "mtk/mtk-utils.h"
 
 #undef __MTK_H_INSIDE__