Walk up slopes smoothly, texture freeing improvement

* Fix collision detection to allow actors to walk up slopes smoothly, without
  losing any horizontal velocity.
* Fix scrolling a level canvas so that chunks near the right or bottom edge
  of the viewpoint were getting culled prematurely.
* Centralize JavaScript exception catching logic to attach Go and JS stack
  traces where possible to be more useful for debugging.
* Performance: flush all SDL2 textures from memory between scene transitions
  in the app. Also add a `flush-textures` dev console command to flush the
  textures at any time - they all should regenerate if still needed based on
  underlying go.Images which can be garbage collected.

Changes.md

@@ -32,8 +32,15 @@ Some minor changes:
       the ground in order to overcome the constant (fast) gravity.
     * Coyote time where the player can still jump a few frames late when they
       walk off a cliff and jump late.
+    * Improved character speed when walking up slopes, they will now travel
+      horizontally at their regular speed instead of being slowed down by level
+      collision every step of the way.
 * Sound effects are now preferred to be in OGG format over MP3 as it is more
   reliable to compile the game cross-platform without the dependency on mpg123.
+* Fix a bug where level chunks on the far right and bottom edge of the screen
+  would flicker out of existence while the level scrolls.
+* When JavaScript exceptions are caught in doodad scripts, the error message
+  will now include the Go and JavaScript stack traces to help with debugging.
 * The game window maximizes on startup to fill the screen.
 
 ## v0.13.2 (Dec 2 2023)

pkg/collision/collide_level.go

@@ -78,6 +78,7 @@ func CollidesWithGrid(d Actor, grid *level.Chunker, target render.Point) (*Colli
 	// e.g.: Boy's Canvas size is 56x56 but he is a narrower character with a
 	// hitbox width smaller than its Canvas size.
 	S = SizePlusHitbox(GetBoundingRect(d), hitbox)
+	actorHeight := P.Y + S.H
 
 	// Test if we are ALREADY colliding with level geometry and try and wiggle
 	// free. ScanBoundingBox scans level pixels along the four edges of the
@@ -120,20 +121,16 @@ func CollidesWithGrid(d Actor, grid *level.Chunker, target render.Point) (*Colli
 
 	// Cap our horizontal movement if we're touching walls.
 	if (result.Left && target.X < P.X) || (result.Right && target.X > P.X) {
-		// If the step is short enough, try and jump up.
-		height := P.Y + S.H
-		if result.Left { // && target.X < P.X {
-			height -= result.LeftPoint.Y
-		} else {
-			height -= result.RightPoint.Y
+		// Handle walking up slopes, if the step is short enough.
+		var slopeHeight int
+		if result.Left {
+			slopeHeight = result.LeftPoint.Y
+		} else if result.Right {
+			slopeHeight = result.RightPoint.Y
 		}
-		if height <= balance.SlopeMaxHeight {
-			target.Y -= height
-			if target.X < P.X {
-				target.X-- // push along to the left
-			} else if target.X > P.X {
-				target.X++ // push along to the right
-			}
+
+		if offset, ok := CanStepUp(actorHeight, slopeHeight, target.X > P.X); ok {
+			target.Add(offset)
 		} else {
 			// Not a slope.. may be a solid wall. If the wall is a SemiSolid though,
 			// do not cap our direction just yet.
@@ -198,13 +195,20 @@ func CollidesWithGrid(d Actor, grid *level.Chunker, target render.Point) (*Colli
 			// for regular solid slopes too. But if this block of code is dummied out for
 			// solid walls, the player is able to clip thru thin walls (couple px thick); the
 			// capLeft/capRight behavior is good at stopping the player here.
+
+			// See if they have hit a solid wall on their left or right edge. If the wall
+			// is short enough to step up, allow them to pass through.
 			if result.Left && !hitLeft && !result.LeftPixel.SemiSolid {
-				hitLeft = true
-				capLeft = result.LeftPoint.X
+				if _, ok := CanStepUp(actorHeight, result.LeftPoint.Y, false); !ok {
+					hitLeft = true
+					capLeft = result.LeftPoint.X
+				}
 			}
 			if result.Right && !hitRight && !result.RightPixel.SemiSolid {
-				hitRight = true
-				capRight = result.RightPoint.X - S.W
+				if _, ok := CanStepUp(actorHeight, result.RightPoint.Y, false); !ok {
+					hitRight = true
+					capRight = result.RightPoint.X - S.W
+				}
 			}
 		}
 
@@ -234,6 +238,37 @@ func CollidesWithGrid(d Actor, grid *level.Chunker, target render.Point) (*Colli
 	return result, result.IsColliding()
 }
 
+/*
+CanStepUp checks whether the actor is moving left or right onto a gentle slope which
+they can step on top of instead of being blocked by the solid wall.
+
+* actorHeight is the actor's Y position + their hitbox height.
+* slopeHeight is the Y position of the left or right edge of the level they collide with.
+* moveRight is true if moving right, false if moving left.
+
+If the actor can step up the slope, the return value is the Point of how to offset their
+X,Y position to move up the slope and the boolean is whether they can step up.
+*/
+func CanStepUp(actorHeight, slopeHeight int, moveRight bool) (render.Point, bool) {
+	var (
+		height = actorHeight - slopeHeight
+		target render.Point
+	)
+
+	if height <= balance.SlopeMaxHeight {
+		target.Y -= height
+		if moveRight {
+			target.X++
+		} else {
+			target.X--
+		}
+
+		return target, true
+	}
+
+	return target, false
+}
+
 // IsColliding returns whether any sort of collision has occurred.
 func (c *Collide) IsColliding() bool {
 	return c.Top || c.Bottom || (c.Left && !c.LeftPixel.SemiSolid) || (c.Right && !c.RightPixel.SemiSolid) ||

pkg/commands.go

@@ -14,6 +14,7 @@ import (
 	"git.kirsle.net/SketchyMaze/doodle/pkg/enum"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/log"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/modal"
+	"git.kirsle.net/SketchyMaze/doodle/pkg/native"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/scripting/exceptions"
 	"github.com/dop251/goja"
 )
@@ -112,6 +113,10 @@ func (c Command) Run(d *Doodle) error {
 				"Filename: trapdoor-down.doodad\n" +
 				"Position: 643,266",
 		)
+	case "flush-textures":
+		// Flush all textures.
+		native.FreeTextures(d.Engine)
+		d.Flash("All textures freed.")
 	default:
 		return c.Default(d)
 	}

pkg/level/chunker.go

@@ -191,8 +191,8 @@ func (c *Chunker) IterViewportChunks(viewport render.Rect) <-chan render.Point {
 			size = int(c.Size)
 		)
 
-		for x := viewport.X; x < viewport.W; x += (size / 4) {
-			for y := viewport.Y; y < viewport.H; y += (size / 4) {
+		for x := viewport.X; x < viewport.W+size; x += (size / 4) {
+			for y := viewport.Y; y < viewport.H+size; y += (size / 4) {
 
 				// Constrain this chunksize step to a point within the bounds
 				// of the viewport. This can yield partial chunks on the edges

pkg/native/engine_sdl.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"image"
 
+	"git.kirsle.net/SketchyMaze/doodle/pkg/log"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/shmem"
 	"git.kirsle.net/go/render"
 	"git.kirsle.net/go/render/sdl"
@@ -43,6 +44,16 @@ func CountTextures(e render.Engine) string {
 	return texCount
 }
 
+// FreeTextures will free all SDL2 textures currently in memory.
+func FreeTextures(e render.Engine) {
+	if sdl, ok := e.(*sdl.Renderer); ok {
+		texCount := sdl.FreeTextures()
+		if texCount > 0 {
+			log.Info("FreeTextures: %d SDL2 textures freed", texCount)
+		}
+	}
+}
+
 /*
 TextToImage takes an SDL2_TTF texture and makes it into a Go image.
 

pkg/native/engine_wasm.go

@@ -26,4 +26,6 @@ func CountTextures(e render.Engine) string {
 	return "n/a"
 }
 
+func FreeTextures() {}
+
 func MaximizeWindow(e render.Engine) {}

pkg/scene.go

@@ -3,6 +3,7 @@ package doodle
 import (
 	"git.kirsle.net/SketchyMaze/doodle/pkg/gamepad"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/log"
+	"git.kirsle.net/SketchyMaze/doodle/pkg/native"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/scripting/exceptions"
 	"git.kirsle.net/go/render/event"
 )
@@ -39,6 +40,9 @@ func (d *Doodle) Goto(scene Scene) error {
 	// Teardown exceptions modal (singleton windows so it can clean up).
 	exceptions.Teardown()
 
+	// Flush all SDL2 textures between scenes.
+	native.FreeTextures(d.Engine)
+
 	log.Info("Goto Scene: %s", scene.Name())
 	d.Scene = scene
 	return d.Scene.Setup(d)

pkg/scripting/events.go

@@ -5,7 +5,6 @@ import (
 	"sync"
 
 	"git.kirsle.net/SketchyMaze/doodle/pkg/keybind"
-	"git.kirsle.net/SketchyMaze/doodle/pkg/log"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/scripting/exceptions"
 	"github.com/dop251/goja"
 )
@@ -107,7 +106,7 @@ func (e *Events) run(name string, args ...interface{}) error {
 			// TODO EXCEPTIONS: I once saw a "runtime error: index out of range [-1]"
 			// from an OnCollide handler between azu-white and thief that was crashing
 			// the app, report this upstream nicely to the user.
-			exceptions.Catch("PANIC: JS %s handler: %s", name, err)
+			exceptions.FormatAndCatch(e.vm.vm, "PANIC: JS %s handler (%s): %s", name, e.vm.Name, err)
 		}
 	}()
 
@@ -126,13 +125,13 @@ func (e *Events) run(name string, args ...interface{}) error {
 			// TODO EXCEPTIONS: this err is useful like
 			// `ReferenceError: playerSpeed is not defined at <eval>:173:9(93)`
 			// but wherever we're returning the err to isn't handling it!
-			exceptions.Catch(
+			exceptions.FormatAndCatch(
+				e.vm.vm,
 				"Scripting error in %s for %s:\n\n%s",
 				name,
 				e.vm.Name,
 				err,
 			)
-			log.Error("Scripting error on %s: %s", name, err)
 			return err
 		}
 

pkg/scripting/exceptions/exceptions.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 	"sync"
 
+	"git.kirsle.net/SketchyMaze/doodle/lib/debugging"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/balance"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/log"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/native"
@@ -13,6 +14,7 @@ import (
 	"git.kirsle.net/go/render"
 	"git.kirsle.net/go/render/event"
 	"git.kirsle.net/go/ui"
+	"github.com/dop251/goja"
 )
 
 // The exception catching window is a singleton and appears on top with
@@ -61,6 +63,38 @@ func Catch(exc string, args ...interface{}) {
 	*excLabel = trim(exc)
 }
 
+// FormatAndCatch an exception from a JavaScript VM. This is the common function called
+// immediately when a scripting-related panic is recovered, and appends stack trace frames
+// and formats the message for final Catch display.
+func FormatAndCatch(vm *goja.Runtime, exc string, args ...interface{}) {
+	// Collect the JavaScript stack frame for debugging.
+	var (
+		buf       [1000]goja.StackFrame
+		jsCallers = []string{}
+		sections  = []string{
+			fmt.Sprintf(exc, args...),
+		}
+	)
+
+	if vm != nil {
+		frames := vm.CaptureCallStack(1000, buf[:0])
+		for i, frame := range frames {
+			var position = frame.Position()
+			jsCallers = append(jsCallers, fmt.Sprintf("%d. %s at %s line %d column %d", i+1, frame.FuncName(), position.Filename, position.Line, position.Column))
+		}
+
+		if len(jsCallers) > 0 {
+			sections = append(sections, fmt.Sprintf("JS stack:\n%s", strings.Join(jsCallers, "\n")))
+		}
+	}
+
+	sections = append(sections, fmt.Sprintf("Go stack:\n%s", debugging.StringifyCallers()))
+
+	Catch(
+		strings.Join(sections, "\n\n"),
+	)
+}
+
 // Setup the global supervisor and window the first time - after the render engine has initialized,
 // e.g., when you want the window to show up the first time.
 func Setup() {

pkg/scripting/pubsub.go

@@ -1,7 +1,6 @@
 package scripting
 
 import (
-	"git.kirsle.net/SketchyMaze/doodle/lib/debugging"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/log"
 	"git.kirsle.net/SketchyMaze/doodle/pkg/scripting/exceptions"
 	"github.com/dop251/goja"
@@ -28,9 +27,7 @@ func RegisterPublishHooks(s *Supervisor, vm *VM) {
 		// Catch any exceptions raised by the JavaScript VM.
 		defer func() {
 			if err := recover(); err != nil {
-				// TODO EXCEPTIONS
-				exceptions.Catch("RegisterPublishHooks(%s): %s", vm.Name, err)
-				debugging.PrintCallers()
+				exceptions.FormatAndCatch(vm.vm, "RegisterPublishHooks(%s): %s: %s", vm.Name, err)
 			}
 		}()
 

pkg/uix/canvas_actors.go

@@ -127,7 +127,8 @@ func (w *Canvas) InstallScripts() error {
 
 		// Call the main() function.
 		if err := vm.Main(); err != nil {
-			exceptions.Catch(
+			exceptions.FormatAndCatch(
+				nil,
 				"Error in main() for actor %s:\n\n%s\n\nActor ID: %s\nFilename: %s\nPosition: %s",
 				actor.Actor.Filename,
 				err,