feat Add z index when rendering sprites

* src/sprite.cpp: Add a new parameter to sprites to define the z index
of the image being rendered.
* src/vk/graphics_pipeline_2d_solid.cpp: Sort may not be the most
efficient algorithm, but it is easier to implement. If this code becomes
slow, it can be optimized with little or no changes to the Ruby
interface.

1 files changed, 40 insertions, 0 deletions

diff --git a/src/vk/sprite_to_draw.cpp b/src/vk/sprite_to_draw.cpp
new file mode 100644
index 0000000..76ee847
--- /dev/null
+++ b/src/vk/sprite_to_draw.cpp
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2022-2023 Frederico de Oliveira Linhares
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "sprite_to_draw.hpp"
+
+namespace VK
+{
+  SpriteToDraw::SpriteToDraw(
+    std::shared_ptr<Sprite> sprite, const glm::vec4 &position, float z_index):
+    sprite{sprite},
+    position{position},
+    z_index{z_index}
+  {
+  }
+
+  bool
+  operator<(const SpriteToDraw& a, const SpriteToDraw& b)
+  {
+    return a.z_index < b.z_index;
+  }
+
+  bool
+  operator>(const SpriteToDraw& a, const SpriteToDraw& b)
+  {
+    return a.z_index > b.z_index;
+  }
+}