graphics: Bug fix: fullscreen rendering was wrong

After fad65f2f5d, the viewport size
is always same as the framebuffer size. The 'screen' image size
was the actual rendering region size, and padding was not
considered in the size. The padding is added on the fullscreen
mode.

This fix adds the extra padding values to the 'screen' image size
so that the 'screen' framebuffer will be same size as the monitor
size.

Fixes #693

graphicscontext.go

@@ -15,8 +15,9 @@
 package ebiten
 
 import (
+	"math"
+
 	"github.com/hajimehoshi/ebiten/internal/clock"
-	"github.com/hajimehoshi/ebiten/internal/graphics"
 	"github.com/hajimehoshi/ebiten/internal/hooks"
 	"github.com/hajimehoshi/ebiten/internal/shareable"
 	"github.com/hajimehoshi/ebiten/internal/ui"
@@ -33,6 +34,8 @@ type graphicsContext struct {
 	f            func(*Image) error
 	offscreen    *Image
 	screen       *Image
+	screenWidth  int
+	screenHeight int
 	screenScale  float64
 	initialized  bool
 	invalidated  bool // browser only
@@ -61,8 +64,10 @@ func (c *graphicsContext) SetSize(screenWidth, screenHeight int, screenScale flo
 
 	w := int(float64(screenWidth) * screenScale)
 	h := int(float64(screenHeight) * screenScale)
-	px0, py0, _, _ := ui.ScreenPadding()
+	px0, py0, px1, py1 := ui.ScreenPadding()
-	c.screen = newImageWithScreenFramebuffer(w, h)
+	c.screen = newImageWithScreenFramebuffer(w+int(math.Ceil(px0+px1)), h+int(math.Ceil(py0+py1)))
+	c.screenWidth = w
+	c.screenHeight = h
 
 	c.offsetX = px0
 	c.offsetY = py0
@@ -110,20 +115,18 @@ func (c *graphicsContext) Update(afterFrameUpdate func()) error {
 	if c.offsetX > 0 || c.offsetY > 0 {
 		op := &DrawImageOptions{}
 		w, h := emptyImage.Size()
-		s := float64(graphics.MaxImageSize())
+		sw, sh := c.screen.Size()
-		op.GeoM.Scale(s/float64(w), s/float64(h))
+		op.GeoM.Scale(float64(sw)/float64(w), float64(sh)/float64(h))
 		op.CompositeMode = CompositeModeCopy
 		c.screen.DrawImage(emptyImage, op)
 	}
 
-	_, dh := c.screen.Size()
-
 	op := &DrawImageOptions{}
 	// c.screen is special: its Y axis is down to up,
 	// and the origin point is lower left.
 	op.GeoM.Scale(c.screenScale, -c.screenScale)
-	// Make dh an even number to fit the upper side of the screen (#662).
+	// Make the screen height an even number to fit the upper side of the screen (#662).
-	op.GeoM.Translate(0, float64((dh+1)/2*2))
+	op.GeoM.Translate(0, float64((c.screenHeight+1)/2*2))
 	op.GeoM.Translate(c.offsetX, c.offsetY)
 
 	op.CompositeMode = CompositeModeCopy

internal/ui/ui_glfw.go

@@ -380,17 +380,24 @@ func ScreenPadding() (x0, y0, x1, y1 float64) {
 		ox := (float64(u.windowWidth)*u.actualScreenScale() - float64(u.width)*u.actualScreenScale()) / 2
 		return ox, 0, ox, 0
 	}
-	ox := 0.0
+
-	oy := 0.0
 	m := glfw.GetPrimaryMonitor()
 	v := m.GetVideoMode()
 	d := devicescale.DeviceScale()
+
+	mx := float64(v.Width) * d / glfwScale()
+	my := float64(v.Height) * d / glfwScale()
+	sx := 0.0
+	sy := 0.0
+
 	_ = u.runOnMainThread(func() error {
-		ox = (float64(v.Width)*d/glfwScale() - float64(u.width)*u.actualScreenScale()) / 2
+		sx = float64(u.width) * u.actualScreenScale()
-		oy = (float64(v.Height)*d/glfwScale() - float64(u.height)*u.actualScreenScale()) / 2
+		sy = float64(u.height) * u.actualScreenScale()
 		return nil
 	})
-	return ox, oy, ox, oy
+	ox := (mx - sx) / 2
+	oy := (my - sy) / 2
+	return ox, oy, (mx - sx) - ox, (my - sy) - oy
 }
 
 func AdjustedCursorPosition() (x, y int) {