X-Git-Url: http://nitlanguage.org

diff --git a/lib/gamnit/flat/flat_core.nit b/lib/gamnit/flat/flat_core.nit
index cd1d11d..800b3de 100644
--- a/lib/gamnit/flat/flat_core.nit
+++ b/lib/gamnit/flat/flat_core.nit
@@ -26,8 +26,6 @@ import gamnit
 intrude import gamnit::cameras
 intrude import gamnit::cameras_cache
 import gamnit::dynamic_resolution
-import gamnit::limit_fps
-import gamnit::camera_control
 
 # Visible 2D entity in the game world or UI
 #
@@ -243,6 +241,32 @@ class Sprite
 		tint_direct = value
 	end
 
+	# Draw order, higher values cause this sprite to be drawn latter
+	#
+	# Change this value to avoid artifacts when drawing non-opaque sprites.
+	# In general, sprites with a non-opaque `texture` and sprites closer to
+	# the camera should have a higher value to be drawn last.
+	#
+	# Sprites sharing a `draw_order` are drawn in the same pass.
+	# The sprite to sprite draw order is undefined and may change when adding
+	# and removing sprites, or changing their attributes.
+	#
+	# ### Warning
+	#
+	# Changing this value may have a negative performance impact if there are
+	# many different `draw_order` values across many sprites.
+	# Sprites sharing some attributes are drawn as group to reduce
+	# the communication overhead between the CPU and GPU,
+	# and changing `draw_order` may break up large groups into smaller groups.
+	var draw_order = 0 is writable(draw_order_direct=)
+
+	# Set draw order,  see `draw_order`
+	fun draw_order=(value: Int)
+	do
+		if isset _draw_order and value != draw_order then needs_remap
+		draw_order_direct = value
+	end
+
 	# Is this sprite static and added in bulk?
 	#
 	# Set to `true` to give a hint to the framework that this sprite won't
@@ -354,10 +378,10 @@ redef class App
 	var ui_camera = new UICamera(app.display.as(not null)) is lazy
 
 	# World sprites drawn as seen by `world_camera`
-	var sprites: Set[Sprite] = new SpriteSet
+	var sprites = new SpriteSet
 
 	# UI sprites drawn as seen by `ui_camera`, over world `sprites`
-	var ui_sprites: Set[Sprite] = new SpriteSet
+	var ui_sprites = new SpriteSet
 
 	# Main method to refine in clients to update game logic and `sprites`
 	fun update(dt: Float) do end
@@ -513,7 +537,7 @@ redef class App
 	# Draw world sprites from `sprites`
 	protected fun frame_core_world_sprites(display: GamnitDisplay)
 	do
-		frame_core_sprites(display, sprites.as(SpriteSet), world_camera)
+		frame_core_sprites(display, sprites, world_camera)
 	end
 
 	# Draw UI sprites from `ui_sprites`
@@ -522,7 +546,7 @@ redef class App
 		# Reset only the depth buffer
 		glClear gl_DEPTH_BUFFER_BIT
 
-		frame_core_sprites(display, ui_sprites.as(SpriteSet), ui_camera)
+		frame_core_sprites(display, ui_sprites, ui_camera)
 	end
 end
 
@@ -851,26 +875,26 @@ redef class OffsetPoint3d
 end
 
 # Set of sprites sorting them into different `SpriteContext`
-private class SpriteSet
+class SpriteSet
 	super HashSet[Sprite]
 
-	# Map texture then static vs dynamic to a `SpriteContext`
-	var contexts_map = new HashMap3[RootTexture, nullable RootTexture, Bool, Array[SpriteContext]]
-
-	# Contexts in `contexts_map`
-	var contexts_items = new Array[SpriteContext]
-
-	# Sprites needing resorting in `contexts_map`
-	var sprites_to_remap = new Array[Sprite]
-
 	# Animation speed multiplier (0.0 to pause, 1.0 for normal speed, etc.)
 	var time_mod = 1.0 is writable
 
 	# Seconds elapsed since the launch of the program, in world time responding to `time_mod`
 	var time = 0.0
 
+	# Map texture then static vs dynamic to a `SpriteContext`
+	private var contexts_map = new HashMap4[RootTexture, nullable RootTexture, Bool, Int, Array[SpriteContext]]
+
+	# Contexts in `contexts_map`, sorted by draw order
+	private var contexts_items = new Array[SpriteContext]
+
+	# Sprites needing resorting in `contexts_map`
+	private var sprites_to_remap = new Array[Sprite]
+
 	# Add a sprite to the appropriate context
-	fun map_sprite(sprite: Sprite)
+	private fun map_sprite(sprite: Sprite)
 	do
 		assert sprite.context == null else print_error "Sprite {sprite} belongs to another SpriteSet"
 
@@ -879,7 +903,8 @@ private class SpriteSet
 		var animation = sprite.animation
 		var animation_texture = if animation != null then
 			animation.frames.first.root else null
-		var contexts = contexts_map[texture, animation_texture, sprite.static]
+		var draw_order = sprite.draw_order
+		var contexts = contexts_map[texture, animation_texture, sprite.static, draw_order]
 
 		var context = null
 		if contexts != null then
@@ -894,15 +919,17 @@ private class SpriteSet
 
 		if context == null then
 			var usage = if sprite.static then gl_STATIC_DRAW else gl_DYNAMIC_DRAW
-			context = new SpriteContext(texture, animation_texture, usage)
+			context = new SpriteContext(texture, animation_texture, usage, draw_order)
 
 			if contexts == null then
 				contexts = new Array[SpriteContext]
-				contexts_map[texture, animation_texture, sprite.static] = contexts
+				contexts_map[texture, animation_texture, sprite.static, draw_order] = contexts
 			end
 
 			contexts.add context
+
 			contexts_items.add context
+			sprite_draw_order_sorter.sort(contexts_items)
 		end
 
 		context.sprites.add sprite
@@ -919,7 +946,7 @@ private class SpriteSet
 	end
 
 	# Remove a sprite from its context
-	fun unmap_sprite(sprite: Sprite)
+	private fun unmap_sprite(sprite: Sprite)
 	do
 		var context = sprite.context
 		assert context != null
@@ -930,14 +957,16 @@ private class SpriteSet
 	end
 
 	# Draw all sprites by all contexts
-	fun draw
+	private fun draw
 	do
+		# Remap sprites that may need to change context
 		for sprite in sprites_to_remap do
 			unmap_sprite sprite
 			map_sprite sprite
 		end
 		sprites_to_remap.clear
 
+		# Sort by draw order
 		for context in contexts_items do context.draw
 	end
 
@@ -990,6 +1019,9 @@ private class SpriteContext
 	# OpenGL ES usage of `buffer_array` and `buffer_element`
 	var usage: GLBufferUsage
 
+	# Draw order shared by all `sprites`
+	var draw_order: Int
+
 	# Sprites drawn by this context
 	var sprites = new GroupedSprites
 
@@ -1179,8 +1211,12 @@ private class SpriteContext
 				data[o+36] = tc[v*2+1]
 
 				# a_tex_diff
-				var dx = animation.frames[1].texture_coords[0] - animation.frames[0].texture_coords[0]
-				var dy = animation.frames[1].texture_coords[1] - animation.frames[0].texture_coords[1]
+				var dx = 0.0
+				var dy = 0.0
+				if animation.frames.length > 1 then
+					dx = animation.frames[1].texture_coords[0] - animation.frames[0].texture_coords[0]
+					dy = animation.frames[1].texture_coords[1] - animation.frames[0].texture_coords[1]
+				end
 				data[o+37] = dx
 				data[o+38] = dy
 
@@ -1698,3 +1734,20 @@ redef class NativeGLfloatArray
 			self[i+dst_offset] = (GLfloat)matrix[i];
 	`}
 end
+
+redef class Sys
+	private var sprite_draw_order_sorter = new DrawOrderComparator is lazy
+end
+
+# Sort `SpriteContext` by their `draw_order`
+private class DrawOrderComparator
+	super Comparator
+
+	# This class can't set COMPARED because
+	# `the public property cannot contain the private type...`
+	#redef type COMPARED: SpriteContext
+
+	# Require: `a isa SpriteContext and b isa SpriteContext`
+	redef fun compare(a, b)
+	do return a.as(SpriteContext).draw_order <=> b.as(SpriteContext).draw_order
+end