changed the way window scaling is done

to support high DPI scaling, use the FramebufferSize functions in glfwcanvas and sdlcanvas to determine the canvas size

examples/drawing/drawing.go

@@ -33,6 +33,20 @@ func main() {
 		cv.SetFillStyle("#000")
 		cv.FillRect(0, 0, w, h)
 
+		// Estimated size used for scaling
+		const (
+			contentWidth  = 1000
+			contentHeight = 350
+		)
+
+		// Calculate scaling
+		sx := w / contentWidth
+		sy := h / contentHeight
+		scale := math.Min(sx, sy)
+		cv.Save()
+		defer cv.Restore()
+		cv.Scale(scale, scale)
+
 		// Draw lines with different colors and line thickness
 		for x := 1.0; x < 10.5; x += 1.0 {
 			cv.SetStrokeStyle(int(x*25), 255, 255)

glfwcanvas/glfwcanvas.go

@@ -33,8 +33,6 @@ type Window struct {
 	KeyUp      func(scancode int, rn rune, name string)
 	KeyChar    func(rn rune)
 	SizeChange func(w, h int)
-	scalex     float64
-	scaley     float64
 }
 
 // CreateWindow creates a window using SDL and initializes the OpenGL context
@@ -79,8 +77,6 @@ func CreateWindow(w, h int, title string) (*Window, *canvas.Canvas, error) {
 	wnd := &Window{
 		Window: window,
 		canvas: cv,
-		scalex: float64(fbw) / float64(w),
-		scaley: float64(fbh) / float64(h),
 	}
 
 	var mx, my int
@@ -93,7 +89,7 @@ func CreateWindow(w, h int, title string) (*Window, *canvas.Canvas, error) {
 		}
 	})
 	window.SetCursorPosCallback(func(w *glfw.Window, xpos, ypos float64) {
-		mx, my = int(math.Round(xpos*wnd.scalex)), int(math.Round(ypos*wnd.scaley))
+		mx, my = int(math.Round(xpos)), int(math.Round(ypos))
 		if wnd.MouseMove != nil {
 			wnd.MouseMove(mx, my)
 		}
@@ -116,12 +112,10 @@ func CreateWindow(w, h int, title string) (*Window, *canvas.Canvas, error) {
 		}
 	})
 	window.SetSizeCallback(func(w *glfw.Window, width, height int) {
-		fbw, fbh := window.GetFramebufferSize()
-		wnd.scalex = float64(fbw) / float64(width)
-		wnd.scaley = float64(fbh) / float64(height)
 		if wnd.SizeChange != nil {
 			wnd.SizeChange(width, height)
 		} else {
+			fbw, fbh := window.GetFramebufferSize()
 			backend.SetBounds(0, 0, fbw, fbh)
 		}
 	})
@@ -168,25 +162,23 @@ func (wnd *Window) FinishFrame() {
 func (wnd *Window) MainLoop(run func()) {
 	for !wnd.close {
 		wnd.StartFrame()
-		if wnd.scalex != 1 || wnd.scaley != 1 {
-			wnd.canvas.Save()
-			wnd.canvas.Scale(wnd.scalex, wnd.scaley)
-		}
 		run()
-		if wnd.scalex != 1 || wnd.scaley != 1 {
-			wnd.canvas.Restore()
-		}
 		wnd.FinishFrame()
 	}
 }
 
-// Size returns the current width and height of the window
+// Size returns the current width and height of the window.
+// Note that this size may not be the same as the size of the
+// framebuffer, since some operating systems scale the window.
+// Use the Width/Height/Size function on Canvas to determine
+// the drawing size
 func (wnd *Window) Size() (int, int) {
 	return wnd.Window.GetSize()
 }
 
 // FramebufferSize returns the current width and height of
-// the framebuffer
+// the framebuffer, which is also the internal size of the
+// canvas
 func (wnd *Window) FramebufferSize() (int, int) {
 	return wnd.Window.GetFramebufferSize()
 }

sdlcanvas/sdlcanvas.go

@@ -5,7 +5,6 @@ import (
 	_ "image/gif" // Imported here so that applications based on this package support these formats by default
 	_ "image/jpeg"
 	_ "image/png"
-	"math"
 	"runtime"
 	"time"
 	"unicode/utf8"
@@ -39,8 +38,6 @@ type Window struct {
 	KeyUp      func(scancode int, rn rune, name string)
 	KeyChar    func(rn rune)
 	SizeChange func(w, h int)
-	scalex     float64
-	scaley     float64
 }
 
 // CreateWindow creates a window using SDL and initializes the OpenGL context
@@ -108,8 +105,6 @@ func CreateWindow(w, h int, title string) (*Window, *canvas.Canvas, error) {
 		Backend:   backend,
 		canvas:    cv,
 		events:    make([]sdl.Event, 0, 100),
-		scalex:    float64(fbw) / float64(w),
-		scaley:    float64(fbh) / float64(h),
 	}
 
 	return wnd, cv, nil
@@ -150,27 +145,23 @@ func (wnd *Window) StartFrame() error {
 		case *sdl.MouseButtonEvent:
 			if e.Type == sdl.MOUSEBUTTONDOWN {
 				if wnd.MouseDown != nil {
-					mx, my := wnd.mpos(e.X, e.Y)
-					wnd.MouseDown(int(e.Button), mx, my)
+					wnd.MouseDown(int(e.Button), int(e.X), int(e.Y))
 					handled = true
 				}
 			} else if e.Type == sdl.MOUSEBUTTONUP {
 				if wnd.MouseUp != nil {
-					mx, my := wnd.mpos(e.X, e.Y)
-					wnd.MouseUp(int(e.Button), mx, my)
+					wnd.MouseUp(int(e.Button), int(e.X), int(e.Y))
 					handled = true
 				}
 			}
 		case *sdl.MouseMotionEvent:
 			if wnd.MouseMove != nil {
-				mx, my := wnd.mpos(e.X, e.Y)
-				wnd.MouseMove(mx, my)
+				wnd.MouseMove(int(e.X), int(e.Y))
 				handled = true
 			}
 		case *sdl.MouseWheelEvent:
 			if wnd.MouseWheel != nil {
-				mx, my := wnd.mpos(e.X, e.Y)
-				wnd.MouseWheel(mx, my)
+				wnd.MouseWheel(int(e.X), int(e.Y))
 				handled = true
 			}
 		case *sdl.KeyboardEvent:
@@ -195,8 +186,6 @@ func (wnd *Window) StartFrame() error {
 			if e.WindowID == wnd.WindowID {
 				if e.Event == sdl.WINDOWEVENT_SIZE_CHANGED {
 					fbw, fbh := wnd.Window.GLGetDrawableSize()
-					wnd.scalex = float64(fbw) / float64(e.Data1)
-					wnd.scaley = float64(fbh) / float64(e.Data2)
 					if wnd.SizeChange != nil {
 						wnd.SizeChange(int(e.Data1), int(e.Data2))
 						handled = true
@@ -220,12 +209,6 @@ func (wnd *Window) StartFrame() error {
 	return nil
 }
 
-func (wnd *Window) mpos(x, y int32) (int, int) {
-	mx := int(math.Round(float64(x) * wnd.scalex))
-	my := int(math.Round(float64(y) * wnd.scaley))
-	return mx, my
-}
-
 // FinishFrame updates the FPS count and displays the frame
 func (wnd *Window) FinishFrame() {
 	now := time.Now()
@@ -267,27 +250,25 @@ func (wnd *Window) MainLoop(run func()) {
 			}
 		}
 
-		if wnd.scalex != 1 || wnd.scaley != 1 {
-			wnd.canvas.Save()
-			wnd.canvas.Scale(wnd.scalex, wnd.scaley)
-		}
 		run()
-		if wnd.scalex != 1 || wnd.scaley != 1 {
-			wnd.canvas.Restore()
-		}
 
 		wnd.FinishFrame()
 	}
 }
 
-// Size returns the current width and height of the window
+// Size returns the current width and height of the window.
+// Note that this size may not be the same as the size of the
+// framebuffer, since some operating systems scale the window.
+// Use the Width/Height/Size function on Canvas to determine
+// the drawing size
 func (wnd *Window) Size() (int, int) {
 	w, h := wnd.Window.GetSize()
 	return int(w), int(h)
 }
 
 // FramebufferSize returns the current width and height of
-// the framebuffer
+// the framebuffer, which is also the internal size of the
+// canvas
 func (wnd *Window) FramebufferSize() (int, int) {
 	w, h := wnd.Window.GLGetDrawableSize()
 	return int(w), int(h)