From e6b71f5512378a01c5fe8226988b6521b511b429 Mon Sep 17 00:00:00 2001
From: Noah Petherbridge <root@kirsle.net>
Date: Sun, 13 Jun 2021 20:25:42 -0700
Subject: [PATCH] Fix Scroll-Follow-Actor Behavior

* The scrollbox by which the game follows the player character has been
  revised, it is now an offset away from the window's center instead of
  fixed pixel distances from the window's edges.
* Mobile form-factor (Pinephone) now scrolls OK instead of jerking back
  and forth rapidly when moving left.
---
 pkg/balance/numbers.go      | 12 ++++++------
 pkg/uix/canvas_scrolling.go | 25 +++++++++++++++----------
 2 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/pkg/balance/numbers.go b/pkg/balance/numbers.go
index 4e2e678..caf7291 100644
--- a/pkg/balance/numbers.go
+++ b/pkg/balance/numbers.go
@@ -1,5 +1,7 @@
 package balance
 
+import "git.kirsle.net/go/render"
+
 // Numbers.
 var (
 	// Window dimensions.
@@ -10,12 +12,10 @@ var (
 	CanvasScrollSpeed = 8
 
 	// Window scrolling behavior in Play Mode.
-	// DEPRECATED: pixels close to window edges
-	ScrollboxHoz  = 256 // horizontal px from window border to start scrol
-	ScrollboxVert = 160
-	// NEW: set scrollbox bounds by percents
-	ScrollboxHozPercent  float64 = 0.25
-	ScrollboxVertPercent float64 = 0.40
+	ScrollboxOffset = render.Point{ // from center of screen
+		X: 40,
+		Y: 100,
+	}
 
 	// Player speeds
 	PlayerMaxVelocity   float64 = 6
diff --git a/pkg/uix/canvas_scrolling.go b/pkg/uix/canvas_scrolling.go
index 456af22..8815405 100644
--- a/pkg/uix/canvas_scrolling.go
+++ b/pkg/uix/canvas_scrolling.go
@@ -6,6 +6,7 @@ import (
 
 	"git.kirsle.net/apps/doodle/pkg/balance"
 	"git.kirsle.net/apps/doodle/pkg/level"
+	"git.kirsle.net/apps/doodle/pkg/shmem"
 	"git.kirsle.net/go/render"
 	"git.kirsle.net/go/render/event"
 )
@@ -110,8 +111,12 @@ func (w *Canvas) loopFollowActor(ev *event.State) error {
 	}
 
 	var (
-		VP = w.Viewport()
-		// ScrollboxHoz = VP.
+		VP            = w.Viewport()
+		engine        = shmem.CurrentRenderEngine
+		Width, Height = engine.WindowSize()
+		midpoint      = render.NewPoint(Width/2, Height/2)
+		scrollboxHoz  = midpoint.X - balance.ScrollboxOffset.X
+		scrollboxVert = midpoint.Y - balance.ScrollboxOffset.Y
 	)
 
 	// Find the actor.
@@ -127,8 +132,8 @@ func (w *Canvas) loopFollowActor(ev *event.State) error {
 		)
 
 		// Scroll left
-		if APosition.X <= VP.X+balance.ScrollboxHoz {
-			var delta = VP.X + balance.ScrollboxHoz - APosition.X
+		if APosition.X <= VP.X+scrollboxHoz {
+			var delta = VP.X + scrollboxHoz - APosition.X
 
 			// constrain in case they're FAR OFF SCREEN so we don't flip back around
 			if delta < 0 {
@@ -138,14 +143,14 @@ func (w *Canvas) loopFollowActor(ev *event.State) error {
 		}
 
 		// Scroll right
-		if APosition.X >= VP.W-ASize.W-balance.ScrollboxHoz {
-			var delta = VP.W - ASize.W - APosition.X - balance.ScrollboxHoz
+		if APosition.X >= VP.W-ASize.W-scrollboxHoz {
+			var delta = VP.W - ASize.W - APosition.X - scrollboxHoz
 			scrollBy.X = delta
 		}
 
 		// Scroll up
-		if APosition.Y <= VP.Y+balance.ScrollboxVert {
-			var delta = VP.Y + balance.ScrollboxVert - APosition.Y
+		if APosition.Y <= VP.Y+scrollboxVert {
+			var delta = VP.Y + scrollboxVert - APosition.Y
 
 			if delta < 0 {
 				delta = -delta
@@ -154,8 +159,8 @@ func (w *Canvas) loopFollowActor(ev *event.State) error {
 		}
 
 		// Scroll down
-		if APosition.Y >= VP.H-ASize.H-balance.ScrollboxVert {
-			var delta = VP.H - ASize.H - APosition.Y - balance.ScrollboxVert
+		if APosition.Y >= VP.H-ASize.H-scrollboxVert {
+			var delta = VP.H - ASize.H - APosition.Y - scrollboxVert
 			if delta > 300 {
 				delta = 300
 			} else if delta < -300 {