From ae0434f7b4ca01e35eba7be8a431981f73c50cb8 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Alexis=20Laferri=C3=A8re?= <alexis.laf@xymus.net>
Date: Fri, 11 Dec 2015 19:25:28 -0500
Subject: [PATCH] lib/gamnit: intro `UICamera`
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Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
---
 lib/gamnit/cameras.nit |   72 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/lib/gamnit/cameras.nit b/lib/gamnit/cameras.nit
index fa23be8..43aae77 100644
--- a/lib/gamnit/cameras.nit
+++ b/lib/gamnit/cameras.nit
@@ -128,3 +128,75 @@ class EulerCamera
 		return view * projection
 	end
 end
+
+# Orthogonal camera to draw UI objects with services to work with screens of different sizes
+#
+# X axis: left to right of the screen, from `position.x` to `position.x + width`
+# Y axis: top to bottom of the screen, from `position.y` to `position.y + height`
+# Z axis: far to near the camera (usually when values are higher), from `far` to `near`
+class UICamera
+	super Camera
+
+	# Clipping wall near the camera, defaults to 100.0
+	var near = 100.0 is writable
+
+	# Clipping wall the farthest of the camera, defaults to -100.0
+	var far: Float = -100.0 is writable
+
+	# Width in world units, defaults to the width in pixels of the screen
+	var width: Float = display.width.to_f is lazy
+
+	# Height in world units, defaults to the height in pixels of the screen
+	var height: Float = display.height.to_f is lazy
+
+	# Reset the camera position so that `height` world units are visible on the Y axis
+	#
+	# By default, `height` is set to `display.height`.
+	#
+	# This can be used to set standardized UI units independently from the screen resolution.
+	fun reset_height(height: nullable Float)
+	do
+		if height == null then height = display.height.to_f
+
+		self.height = height
+		self.width = height * display.aspect_ratio
+	end
+
+	# Convert the position `x, y` on screen, to UI coordinates
+	fun camera_to_ui(x, y: Numeric): Point[Float]
+	do
+		# FIXME this kind of method should use something like a canvas
+		# instead of being hard coded on the display.
+
+		var wx = x.to_f * width / display.width.to_f - position.x
+		var wy = y.to_f * height / display.height.to_f - position.y
+		return new Point[Float](wx, wy)
+	end
+
+	# Anchor in the top left corner of the screen, at z = 0
+	fun top_left: Point3d[Float] do return new Point3d[Float](position.x, position.y, 0.0)
+
+	# Anchor in the top right corner of the screen, at z = 0
+	fun top_right: Point3d[Float] do return new Point3d[Float](position.x + width, position.y, 0.0)
+
+	# Anchor in the bottom left corner of the screen, at z = 0
+	fun bottom_left: Point3d[Float] do return new Point3d[Float](position.x, position.y + height, 0.0)
+
+	# Anchor in the bottom right corner of the screen, at z = 0
+	fun bottom_right: Point3d[Float] do return new Point3d[Float](position.x + width, position.y + height, 0.0)
+
+	# TODO cache the anchors and the matrix
+
+	redef fun mvp_matrix
+	do
+		var view = new Matrix.identity(4)
+
+		# Translate the world away from the camera
+		view.translate(-position.x/2.0, -position.y/2.0, -position.z/2.0)
+
+		# Use a projection matrix with a depth
+		var projection = new Matrix.orthogonal(0.0, width, -height, 0.0, near, far)
+
+		return view * projection
+	end
+end
-- 
1.7.9.5