4 files changed, 19 insertions, 3 deletions
diff --git a/shaders/tile.cpp b/shaders/tile.cpp
index 2fb37cd8..c8261acd 100644
--- a/shaders/tile.cpp
+++ b/shaders/tile.cpp
@@ -1,6 +1,7 @@
 #include "shaders/tile.hpp"
 #include "loader.hpp"
 #include "compat/assert.hpp"
+#include "local-coords.hpp"
 #include <Magnum/Math/Vector4.h>
 #include <Magnum/GL/Context.h>
 #include <Magnum/GL/Shader.h>
@@ -65,4 +66,13 @@ void tile_shader::_draw()
     }
 }
 
+float tile_shader::depth_value(const local_coords& xy) noexcept
+{
+    constexpr float max = (TILE_MAX_DIM+1)*(TILE_MAX_DIM+1) * .5f;
+    constexpr float min = -1 + 1.f/256;
+    float value = min + xy.to_index()/max;
+    fm_assert(value > -1 && value < 1);
+    return value;
+}
+
 } // namespace floormat
diff --git a/shaders/tile.frag b/shaders/tile.frag
index 64372b7b..a233825e 100644
--- a/shaders/tile.frag
+++ b/shaders/tile.frag
@@ -5,6 +5,7 @@ layout (location = 2) uniform vec4 tint = vec4(1, 1, 1, 1);
 
 noperspective in vec2 frag_texcoords;
 out vec4 color;
+//layout (depth_greater) out float gl_FragDepth;
 
 void main() {
     color = texture(sampler, frag_texcoords) * tint;
diff --git a/shaders/tile.hpp b/shaders/tile.hpp
index 2be1414a..8a45e1e7 100644
--- a/shaders/tile.hpp
+++ b/shaders/tile.hpp
@@ -7,10 +7,13 @@
 
 namespace floormat {
 
+struct local_coords;
+
 struct tile_shader : GL::AbstractShaderProgram
 {
-    typedef GL::Attribute<0, Vector3> Position;
-    typedef GL::Attribute<1, Vector2> TextureCoordinates;
+    using Position           = GL::Attribute<0, Vector3>;
+    using TextureCoordinates = GL::Attribute<1, Vector2>;
+    using Depth              = GL::Attribute<2, float>;
 
     fm_DECLARE_DEFAULT_MOVE_ASSIGNMENT_(tile_shader);
     fm_DECLARE_DELETED_COPY_ASSIGNMENT(tile_shader);
@@ -24,6 +27,7 @@ struct tile_shader : GL::AbstractShaderProgram
     tile_shader& set_camera_offset(Vector2d camera_offset);
     Vector4 tint() const { return _tint; }
     tile_shader& set_tint(const Vector4& tint);
+    static float depth_value(const local_coords& xy) noexcept;
 
     template<typename T = float> static constexpr Math::Vector2<T> project(const Math::Vector3<T>& pt);
     template<typename T = float> static constexpr Math::Vector2<T> unproject(const Math::Vector2<T>& px);
diff --git a/shaders/tile.vert b/shaders/tile.vert
index b512b7ac..ad038e6d 100644
--- a/shaders/tile.vert
+++ b/shaders/tile.vert
@@ -5,10 +5,11 @@ layout (location = 1) uniform vec2 offset;
 
 layout (location = 0) in vec4 position;
 layout (location = 1) in vec2 texcoords;
+layout (location = 2) in float depth;
 noperspective out vec2 frag_texcoords;
 
 void main() {
     float x = -position.y, y = -position.x, z = position.z;
-    gl_Position = vec4((x-y+offset.x)*scale.x, ((x+y+z*2)*.59-offset.y)*scale.y, 0, 1);
+    gl_Position = vec4((x-y+offset.x)*scale.x, ((x+y+z*2)*.59-offset.y)*scale.y, depth, 1);
     frag_texcoords = texcoords;
 }