diff --git a/audio/audio.go b/audio/audio.go
index 1af03c037..fa9f4cef0 100644
--- a/audio/audio.go
+++ b/audio/audio.go
@@ -320,7 +320,7 @@ func NewPlayerFromBytes(context *Context, src []byte) (*Player, error) {
 	p, err := NewPlayer(context, b)
 	if err != nil {
 		// Errors should never happen.
-		panic(err)
+		panic(fmt.Sprintf("audio: %v at NewPlayerFromBytes", err))
 	}
 	return p, nil
 }
@@ -418,7 +418,7 @@ func (p *playerImpl) readLoop() {
 		case s := <-p.seekCh:
 			seeker, ok := p.src.(io.Seeker)
 			if !ok {
-				panic("not reached")
+				panic("audio: the source must be io.Seeker when seeking")
 			}
 			pos, err := seeker.Seek(s.offset, s.whence)
 			p.buf = nil
diff --git a/audio/loop.go b/audio/loop.go
index 8e07e85f1..fee14e4a8 100644
--- a/audio/loop.go
+++ b/audio/loop.go
@@ -75,7 +75,7 @@ func (i *InfiniteLoop) Read(b []byte) (int, error) {
 	n, err := i.src.Read(b)
 	i.pos += int64(n)
 	if i.pos > i.length() {
-		panic("not reached")
+		panic(fmt.Sprintf("audio: position must be <= length but not at (*InfiniteLoop).Read: pos: %d, length: %d", i.pos, i.length()))
 	}
 
 	if err != nil && err != io.EOF {
diff --git a/audio/vorbis/internal/stb/decode.go b/audio/vorbis/internal/stb/decode.go
index 9b54cd43f..03dcc1340 100644
--- a/audio/vorbis/internal/stb/decode.go
+++ b/audio/vorbis/internal/stb/decode.go
@@ -69,7 +69,7 @@ func (s *Samples) Read(buf []float32) (int, error) {
 		start = 0
 	}
 	if len(s.samples[idx]) == 0 {
-		panic("not reached")
+		panic(fmt.Sprintf("stb: len(samples[%d]) must be > 0", idx))
 	}
 	n := copy(buf, s.samples[idx][start:])
 	s.posInSamples += int64(n) / int64(s.channels)
diff --git a/graphicscontext.go b/graphicscontext.go
index 95e22913c..484ce076d 100644
--- a/graphicscontext.go
+++ b/graphicscontext.go
@@ -15,6 +15,7 @@
 package ebiten
 
 import (
+	"fmt"
 	"math"
 
 	"github.com/hajimehoshi/ebiten/internal/clock"
@@ -121,7 +122,7 @@ func (c *graphicsContext) Update(afterFrameUpdate func()) error {
 
 	op := &DrawImageOptions{}
 
-	switch graphicscommand.Driver().VDirection() {
+	switch vd := graphicscommand.Driver().VDirection(); vd {
 	case graphicsdriver.VDownward:
 		// c.screen is special: its Y axis is down to up,
 		// and the origin point is lower left.
@@ -130,7 +131,7 @@ func (c *graphicsContext) Update(afterFrameUpdate func()) error {
 	case graphicsdriver.VUpward:
 		op.GeoM.Scale(c.screenScale, c.screenScale)
 	default:
-		panic("not reached")
+		panic(fmt.Sprintf("ebiten: invalid v-direction: %d", vd))
 	}
 
 	op.GeoM.Translate(c.offsetX, c.offsetY)
diff --git a/image.go b/image.go
index 38eeca93a..575b95f3d 100644
--- a/image.go
+++ b/image.go
@@ -44,7 +44,7 @@ func (m *mipmap) original() *shareable.Image {
 
 func (m *mipmap) level(r image.Rectangle, level int) *shareable.Image {
 	if level == 0 {
-		panic("not reached")
+		panic("ebiten: level must not be 0 (original image) at level")
 	}
 
 	imgs, ok := m.imgs[r]
@@ -182,7 +182,7 @@ func (i *Image) Fill(clr color.Color) error {
 
 	// TODO: Implement this.
 	if i.isSubimage() {
-		panic("render to a subimage is not implemented")
+		panic("ebiten: render to a subimage is not implemented (Fill)")
 	}
 
 	i.resolvePixelsToSet(false)
@@ -196,7 +196,7 @@ func (i *Image) Fill(clr color.Color) error {
 
 func (i *Image) disposeMipmaps() {
 	if i.isDisposed() {
-		panic("not reached")
+		panic("ebiten: the image is already disposed at disposeMipmap")
 	}
 	i.mipmap.disposeMipmaps()
 }
@@ -254,7 +254,7 @@ func (i *Image) drawImage(img *Image, options *DrawImageOptions) {
 
 	// TODO: Implement this.
 	if i.isSubimage() {
-		panic("render to a subimage is not implemented")
+		panic("ebiten: render to a subimage is not implemented (drawImage)")
 	}
 
 	img.resolvePixelsToSet(true)
@@ -326,7 +326,7 @@ func (i *Image) drawImage(img *Image, options *DrawImageOptions) {
 		}
 		level = graphics.MipmapLevel(det)
 		if level < 0 {
-			panic("not reached")
+			panic(fmt.Sprintf("ebiten: level must be >= 0 but %d", level))
 		}
 	}
 	if level > 6 {
@@ -443,7 +443,7 @@ func (i *Image) DrawTriangles(vertices []Vertex, indices []uint16, img *Image, o
 	}
 
 	if i.isSubimage() {
-		panic("render to a subimage is not implemented")
+		panic("ebiten: render to a subimage is not implemented (DrawTriangles)")
 	}
 
 	img.resolvePixelsToSet(true)
@@ -663,7 +663,7 @@ func (i *Image) ReplacePixels(p []byte) error {
 	}
 	// TODO: Implement this.
 	if i.isSubimage() {
-		panic("render to a subimage is not implemented")
+		panic("ebiten: render to a subimage is not implemented (ReplacePixels)")
 	}
 	i.resolvePixelsToSet(false)
 	s := i.Bounds().Size()
diff --git a/internal/graphics/compositemode.go b/internal/graphics/compositemode.go
index c649aa966..d3a1d4845 100644
--- a/internal/graphics/compositemode.go
+++ b/internal/graphics/compositemode.go
@@ -14,6 +14,10 @@
 
 package graphics
 
+import (
+	"fmt"
+)
+
 type CompositeMode int
 
 const (
@@ -75,6 +79,6 @@ func (c CompositeMode) Operations() (src Operation, dst Operation) {
 	case CompositeModeLighter:
 		return One, One
 	default:
-		panic("not reached")
+		panic(fmt.Sprintf("graphics: invalid composite mode: %d", c))
 	}
 }
diff --git a/internal/graphics/vertices.go b/internal/graphics/vertices.go
index 48dd1fbd7..d26a2abb9 100644
--- a/internal/graphics/vertices.go
+++ b/internal/graphics/vertices.go
@@ -15,6 +15,7 @@
 package graphics
 
 import (
+	"fmt"
 	"sync"
 )
 
@@ -36,7 +37,7 @@ const (
 func (v *verticesBackend) slice(n int) []float32 {
 	const num = 1024
 	if n > num {
-		panic("not reached")
+		panic(fmt.Sprintf("graphics: n must be <= num but not: n: %d, num: %d", n, num))
 	}
 
 	v.m.Lock()
@@ -67,10 +68,10 @@ func isPowerOf2(x int) bool {
 
 func QuadVertices(width, height int, sx0, sy0, sx1, sy1 int, a, b, c, d, tx, ty float32, cr, cg, cb, ca float32) []float32 {
 	if !isPowerOf2(width) {
-		panic("not reached")
+		panic(fmt.Sprintf("graphics: width must be power of 2 but not at QuadVertices: %d", width))
 	}
 	if !isPowerOf2(height) {
-		panic("not reached")
+		panic(fmt.Sprintf("graphics: height must be power of 2 but not at QuadVertices: %d", height))
 	}
 
 	if sx0 >= sx1 || sy0 >= sy1 {
@@ -166,10 +167,10 @@ func QuadIndices() []uint16 {
 
 func PutVertex(vs []float32, width, height int, dx, dy, su, sv float32, u0, v0, u1, v1 float32, cr, cg, cb, ca float32) {
 	if !isPowerOf2(width) {
-		panic("not reached")
+		panic(fmt.Sprintf("graphics: width must be power of 2 but not at PutVertices: %d", width))
 	}
 	if !isPowerOf2(height) {
-		panic("not reached")
+		panic(fmt.Sprintf("graphics: height must be power of 2 but not at PutVertices: %d", height))
 	}
 
 	vs[0] = dx
diff --git a/internal/graphicscommand/command.go b/internal/graphicscommand/command.go
index 8532ffae5..d36fface0 100644
--- a/internal/graphicscommand/command.go
+++ b/internal/graphicscommand/command.go
@@ -89,7 +89,7 @@ func (q *commandQueue) appendIndices(indices []uint16, offset uint16) {
 
 func (q *commandQueue) doEnqueueDrawImageCommand(dst, src *Image, nvertices, nindices int, color *affine.ColorM, mode graphics.CompositeMode, filter graphics.Filter, address graphics.Address, forceNewCommand bool) {
 	if nindices > graphics.IndicesNum {
-		panic("not reached")
+		panic(fmt.Sprintf("graphicscommand: nindices must be <= graphics.IndicesNum but not at doEnqueueDrawImageCommand: nindices: %d, graphics.IndicesNum: %d", nindices, graphics.IndicesNum))
 	}
 	if !forceNewCommand && 0 < len(q.commands) {
 		if last := q.commands[len(q.commands)-1]; last.CanMerge(dst, src, color, mode, filter, address) {
@@ -114,7 +114,7 @@ func (q *commandQueue) doEnqueueDrawImageCommand(dst, src *Image, nvertices, nin
 // EnqueueDrawImageCommand enqueues a drawing-image command.
 func (q *commandQueue) EnqueueDrawImageCommand(dst, src *Image, vertices []float32, indices []uint16, color *affine.ColorM, mode graphics.CompositeMode, filter graphics.Filter, address graphics.Address) {
 	if len(indices) > graphics.IndicesNum {
-		panic("not reached")
+		panic(fmt.Sprintf("graphicscommand: len(indices) must be <= graphics.IndicesNum but not at EnqueueDrawImageCommand: len(indices): %d, graphics.IndicesNum: %d", len(indices), graphics.IndicesNum))
 	}
 
 	split := false
@@ -156,7 +156,7 @@ func (q *commandQueue) Flush() {
 		nc := 0
 		for _, c := range q.commands {
 			if c.NumIndices() > graphics.IndicesNum {
-				panic("not reached")
+				panic(fmt.Sprintf("graphicscommand: c.NumIndices() must be <= graphics.IndicesNum but not at Flush: c.NumIndices(): %d, graphics.IndicesNum: %d", c.NumIndices(), graphics.IndicesNum))
 			}
 			if ne+c.NumIndices() > graphics.IndicesNum {
 				break
diff --git a/internal/graphicsdriver/metal/driver.go b/internal/graphicsdriver/metal/driver.go
index 61802c802..97b865fc3 100644
--- a/internal/graphicsdriver/metal/driver.go
+++ b/internal/graphicsdriver/metal/driver.go
@@ -460,7 +460,7 @@ func (d *Driver) Reset() error {
 			case graphics.OneMinusDstAlpha:
 				return mtl.BlendFactorOneMinusDestinationAlpha
 			default:
-				panic("not reached")
+				panic(fmt.Sprintf("metal: invalid operation: %d", c))
 			}
 		}
 
@@ -627,7 +627,7 @@ func (i *Image) IsInvalidated() bool {
 func (i *Image) syncTexture() {
 	mainthread.Run(func() error {
 		if i.driver.cb != (mtl.CommandBuffer{}) {
-			panic("not reached")
+			panic("metal: command buffer must be empty at syncTexture: flush is not called yet?")
 		}
 
 		cb := i.driver.cq.MakeCommandBuffer()
diff --git a/internal/graphicsdriver/opengl/context.go b/internal/graphicsdriver/opengl/context.go
index 6ef3da970..e56572855 100644
--- a/internal/graphicsdriver/opengl/context.go
+++ b/internal/graphicsdriver/opengl/context.go
@@ -15,6 +15,8 @@
 package opengl
 
 import (
+	"fmt"
+
 	"github.com/hajimehoshi/ebiten/internal/graphics"
 )
 
@@ -33,7 +35,7 @@ func convertOperation(op graphics.Operation) operation {
 	case graphics.OneMinusDstAlpha:
 		return oneMinusDstAlpha
 	default:
-		panic("not reached")
+		panic(fmt.Sprintf("opengl: invalid operation %d at convertOperation", op))
 	}
 }
 
diff --git a/internal/graphicsdriver/opengl/context_desktop.go b/internal/graphicsdriver/opengl/context_desktop.go
index 4b8ec2e12..f2dbbdc92 100644
--- a/internal/graphicsdriver/opengl/context_desktop.go
+++ b/internal/graphicsdriver/opengl/context_desktop.go
@@ -391,7 +391,7 @@ func (c *context) uniformFloats(p program, location string, v []float32) {
 		case 16:
 			gl.UniformMatrix4fv(l, 1, false, (*float32)(gl.Ptr(v)))
 		default:
-			panic("not reached")
+			panic(fmt.Sprintf("opengl: invalid uniform floats num: %d", len(v)))
 		}
 		return nil
 	})
diff --git a/internal/graphicsdriver/opengl/context_js.go b/internal/graphicsdriver/opengl/context_js.go
index 817a8edf7..ddd13f3cc 100644
--- a/internal/graphicsdriver/opengl/context_js.go
+++ b/internal/graphicsdriver/opengl/context_js.go
@@ -374,7 +374,7 @@ func (c *context) uniformFloats(p program, location string, v []float32) {
 		gl.Call("uniformMatrix4fv", js.Value(l), false, arr)
 		arr.Release()
 	default:
-		panic("not reached")
+		panic(fmt.Sprintf("opengl: invalid uniform floats num: %d", len(v)))
 	}
 }
 
diff --git a/internal/graphicsdriver/opengl/context_mobile.go b/internal/graphicsdriver/opengl/context_mobile.go
index e609144b6..f514ef58d 100644
--- a/internal/graphicsdriver/opengl/context_mobile.go
+++ b/internal/graphicsdriver/opengl/context_mobile.go
@@ -75,7 +75,7 @@ type contextImpl struct {
 
 func (c *context) doWork(chDone <-chan struct{}) error {
 	if c.worker == nil {
-		panic("not reached")
+		panic("opengl: worker must be initialized but not")
 	}
 	// TODO: Check this is called on the rendering thread
 	workAvailable := c.worker.WorkAvailable()
@@ -307,7 +307,7 @@ func (c *context) uniformFloats(p program, location string, v []float32) {
 	case 16:
 		gl.UniformMatrix4fv(l, v)
 	default:
-		panic("not reached")
+		panic(fmt.Sprintf("opengl: invalid uniform floats num: %d", len(v)))
 	}
 }
 
diff --git a/internal/graphicsdriver/opengl/image.go b/internal/graphicsdriver/opengl/image.go
index b3b6dd828..0bb5e58a2 100644
--- a/internal/graphicsdriver/opengl/image.go
+++ b/internal/graphicsdriver/opengl/image.go
@@ -87,8 +87,7 @@ func (i *Image) ensureFramebuffer() error {
 
 func (i *Image) ReplacePixels(p []byte, x, y, width, height int) {
 	if i.screen {
-		// The screen image doesn't have a texture to replace pixels.
-		panic("not reached")
+		panic("opengl: ReplacePixels cannot be called on the screen, that doesn't have a texture")
 	}
 
 	// glFlush is necessary on Android.
diff --git a/internal/graphicsdriver/opengl/shader.go b/internal/graphicsdriver/opengl/shader.go
index 9808847ff..934348c09 100644
--- a/internal/graphicsdriver/opengl/shader.go
+++ b/internal/graphicsdriver/opengl/shader.go
@@ -80,7 +80,7 @@ func shaderStr(id shaderID) string {
 			src = strings.Replace(src, k, v, -1)
 		}
 	default:
-		panic("not reached")
+		panic(fmt.Sprintf("opengl: invalid shader id: %d", id))
 	}
 
 	checkGLSL(src)
diff --git a/internal/graphicsdriver/opengl/types.go b/internal/graphicsdriver/opengl/types.go
index 8ca2d01f5..86692efd4 100644
--- a/internal/graphicsdriver/opengl/types.go
+++ b/internal/graphicsdriver/opengl/types.go
@@ -14,6 +14,10 @@
 
 package opengl
 
+import (
+	"fmt"
+)
+
 type (
 	shaderType  int
 	bufferType  int
@@ -30,6 +34,6 @@ func (d dataType) SizeInBytes() int {
 	case float:
 		return 4
 	default:
-		panic("not reached")
+		panic(fmt.Sprintf("opengl: invalid data type: %d", d))
 	}
 }
diff --git a/internal/packing/packing.go b/internal/packing/packing.go
index d2488ce08..596f683d8 100644
--- a/internal/packing/packing.go
+++ b/internal/packing/packing.go
@@ -130,7 +130,7 @@ func (p *Page) alloc(n *Node, width, height int) *Node {
 		return p.alloc(n.child0, width, height)
 	}
 	if n.child0 == nil || n.child1 == nil {
-		panic("not reached")
+		panic("packing: both two children must not be nil at alloc")
 	}
 	if node := p.alloc(n.child0, width, height); node != nil {
 		return node
@@ -174,7 +174,7 @@ func (p *Page) Free(node *Node) {
 		return
 	}
 	if node.parent.child0 == nil || node.parent.child1 == nil {
-		panic("not reached: double free?")
+		panic("packing: both two children must not be nil at Free: double free happened?")
 	}
 	if node.parent.child0.canFree() && node.parent.child1.canFree() {
 		node.parent.child0 = nil
diff --git a/internal/restorable/image.go b/internal/restorable/image.go
index 0a325c474..89653845c 100644
--- a/internal/restorable/image.go
+++ b/internal/restorable/image.go
@@ -102,7 +102,7 @@ func NewScreenFramebufferImage(width, height int) *Image {
 
 func (i *Image) clear() {
 	if i.priority {
-		panic("not reached")
+		panic("restorable: clear cannot be called on a priority image")
 	}
 
 	// There are not 'drawImageHistoryItem's for this image and dummyImage.
@@ -250,7 +250,7 @@ func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 // DrawImage draws a given image img to the image.
 func (i *Image) DrawImage(img *Image, vertices []float32, indices []uint16, colorm *affine.ColorM, mode graphics.CompositeMode, filter graphics.Filter, address graphics.Address) {
 	if i.priority {
-		panic("not reached")
+		panic("restorable: DrawImage cannot be called on a priority image")
 	}
 	if len(vertices) == 0 {
 		return
@@ -412,9 +412,8 @@ func (i *Image) restore() error {
 		gimg.ReplacePixels(pix, 0, 0, w, h)
 	}
 	for _, c := range i.drawImageHistory {
-		// All dependencies must be already resolved.
 		if c.image.hasDependency() {
-			panic("not reached")
+			panic("restorable: all dependencies must be already resolved but not")
 		}
 		gimg.DrawImage(c.image.image, c.vertices, c.indices, c.colorm, c.mode, c.filter, c.address)
 	}
diff --git a/internal/restorable/images.go b/internal/restorable/images.go
index 6b7df54bb..42e2348d6 100644
--- a/internal/restorable/images.go
+++ b/internal/restorable/images.go
@@ -131,7 +131,7 @@ func (i *images) makeStaleIfDependingOn(target *Image) {
 
 func (i *images) makeStaleIfDependingOnImpl(target *Image) {
 	if target == nil {
-		panic("not reached")
+		panic("restorable: target must not be nil at makeStaleIfDependingOnImpl")
 	}
 	if i.lastTarget == target {
 		return
@@ -147,7 +147,7 @@ func (i *images) makeStaleIfDependingOnImpl(target *Image) {
 // Restoring means to make all *graphicscommand.Image objects have their textures and framebuffers.
 func (i *images) restore() error {
 	if !IsRestoringEnabled() {
-		panic("not reached")
+		panic("restorable: restore cannot be called when restoring is disabled")
 	}
 
 	// Dispose image explicitly
diff --git a/internal/shareable/shareable.go b/internal/shareable/shareable.go
index a1a2ca06b..9058d9743 100644
--- a/internal/shareable/shareable.go
+++ b/internal/shareable/shareable.go
@@ -15,6 +15,7 @@
 package shareable
 
 import (
+	"fmt"
 	"image"
 	"runtime"
 	"sync"
@@ -71,7 +72,7 @@ func (b *backend) TryAlloc(width, height int) (*packing.Node, bool) {
 
 	n := b.page.Alloc(width, height)
 	if n == nil {
-		panic("not reached")
+		panic("shareable: Alloc result must not be nil at TryAlloc")
 	}
 	return n, true
 }
@@ -150,7 +151,7 @@ func (i *Image) forceShared() {
 	}
 
 	if !i.shareable() {
-		panic("not reached")
+		panic("shareable: forceShared cannot be called on a non-shareable image")
 	}
 
 	newI := NewImage(i.width, i.height)
@@ -171,7 +172,7 @@ func (i *Image) forceShared() {
 
 func (i *Image) region() (x, y, width, height int) {
 	if i.backend == nil {
-		panic("not reached")
+		panic("shareable: backend must not be nil: not allocated yet?")
 	}
 	if !i.isShared() {
 		w, h := i.backend.restorable.Size()
@@ -304,7 +305,7 @@ func (i *Image) replacePixels(p []byte) {
 	x, y, w, h := i.region()
 	if p != nil {
 		if l := 4 * w * h; len(p) != l {
-			panic("not reached")
+			panic(fmt.Sprintf("shareable: len(p) must be %d but %d", l, len(p)))
 		}
 	}
 	i.backend.restorable.ReplacePixels(p, x, y, w, h)
@@ -379,7 +380,7 @@ func (i *Image) dispose(markDisposed bool) {
 		}
 	}
 	if index == -1 {
-		panic("not reached")
+		panic("shareable: backend not found at an image being disposed")
 	}
 	theBackends = append(theBackends[:index], theBackends[index+1:]...)
 }
@@ -418,7 +419,7 @@ func (i *Image) shareable() bool {
 
 func (i *Image) allocate(shareable bool) {
 	if i.backend != nil {
-		panic("not reached")
+		panic("shareable: the image is already allocated")
 	}
 
 	if !shareable || !i.shareable() {
@@ -440,7 +441,7 @@ func (i *Image) allocate(shareable bool) {
 	size := initSize
 	for i.width > size || i.height > size {
 		if size == maxSize {
-			panic("not reached")
+			panic(fmt.Sprintf("shareable: the image being shared is too big: width: %d, height: %d", i.width, i.height))
 		}
 		size *= 2
 	}
@@ -453,7 +454,7 @@ func (i *Image) allocate(shareable bool) {
 
 	n := b.page.Alloc(i.width, i.height)
 	if n == nil {
-		panic("not reached")
+		panic("shareable: Alloc result must not be nil at allocate")
 	}
 	i.backend = b
 	i.node = n
diff --git a/internal/ui/ui_glfw.go b/internal/ui/ui_glfw.go
index e18cc4f2b..fd135af13 100644
--- a/internal/ui/ui_glfw.go
+++ b/internal/ui/ui_glfw.go
@@ -280,7 +280,7 @@ func SetScreenSize(width, height int) {
 		panic("ui: Run is not called yet")
 	}
 	_ = mainthread.Run(func() error {
-		u.setScreenSize(width, height, u.scale, u.fullscreen(), u.vsync)
+		u.setScreenSize(width, height, u.scale, u.isFullscreen(), u.vsync)
 		return nil
 	})
 }
@@ -292,7 +292,7 @@ func SetScreenScale(scale float64) bool {
 	}
 	r := false
 	_ = mainthread.Run(func() error {
-		r = u.setScreenSize(u.width, u.height, scale, u.fullscreen(), u.vsync)
+		r = u.setScreenSize(u.width, u.height, scale, u.isFullscreen(), u.vsync)
 		return nil
 	})
 	return r
@@ -311,10 +311,10 @@ func ScreenScale() float64 {
 	return s
 }
 
-// fullscreen must be called from the main thread.
-func (u *userInterface) fullscreen() bool {
+// isFullscreen must be called from the main thread.
+func (u *userInterface) isFullscreen() bool {
 	if !u.isRunning() {
-		panic("not reached")
+		panic("ui: the game must be running at isFullscreen")
 	}
 	return u.window.GetMonitor() != nil
 }
@@ -326,7 +326,7 @@ func IsFullscreen() bool {
 	}
 	b := false
 	_ = mainthread.Run(func() error {
-		b = u.fullscreen()
+		b = u.isFullscreen()
 		return nil
 	})
 	return b
@@ -367,7 +367,7 @@ func SetVsyncEnabled(enabled bool) {
 	}
 	_ = mainthread.Run(func() error {
 		u := currentUI
-		u.setScreenSize(u.width, u.height, u.scale, u.fullscreen(), enabled)
+		u.setScreenSize(u.width, u.height, u.scale, u.isFullscreen(), enabled)
 		return nil
 	})
 }
@@ -646,7 +646,7 @@ func Run(width, height int, scale float64, title string, g GraphicsContext, main
 			s := glfwScale()
 			w := int(float64(width) / u.scale / s)
 			h := int(float64(height) / u.scale / s)
-			if u.fullscreen() {
+			if u.isFullscreen() {
 				return
 			}
 			u.reqWidth = w
@@ -673,7 +673,7 @@ func (u *userInterface) glfwSize() (int, int) {
 
 // getScale must be called from the main thread.
 func (u *userInterface) getScale() float64 {
-	if !u.fullscreen() {
+	if !u.isFullscreen() {
 		return u.scale
 	}
 	if u.fullscreenScale == 0 {
@@ -711,7 +711,7 @@ func (u *userInterface) updateGraphicsContext(g GraphicsContext) {
 	_ = mainthread.Run(func() error {
 		actualScale = u.actualScreenScale()
 		if u.lastActualScale != actualScale {
-			u.forceSetScreenSize(u.width, u.height, u.scale, u.fullscreen(), u.vsync)
+			u.forceSetScreenSize(u.width, u.height, u.scale, u.isFullscreen(), u.vsync)
 		}
 		u.lastActualScale = actualScale
 
@@ -777,7 +777,7 @@ func (u *userInterface) update(g GraphicsContext) error {
 	_ = mainthread.Run(func() error {
 		w, h := u.reqWidth, u.reqHeight
 		if w != 0 || h != 0 {
-			u.setScreenSize(w, h, u.scale, u.fullscreen(), u.vsync)
+			u.setScreenSize(w, h, u.scale, u.isFullscreen(), u.vsync)
 		}
 		u.reqWidth = 0
 		u.reqHeight = 0
@@ -822,7 +822,7 @@ func (u *userInterface) swapBuffers() {
 
 // setScreenSize must be called from the main thread.
 func (u *userInterface) setScreenSize(width, height int, scale float64, fullscreen bool, vsync bool) bool {
-	if u.width == width && u.height == height && u.scale == scale && u.fullscreen() == fullscreen && u.vsync == vsync {
+	if u.width == width && u.height == height && u.scale == scale && u.isFullscreen() == fullscreen && u.vsync == vsync {
 		return false
 	}
 	u.forceSetScreenSize(width, height, scale, fullscreen, vsync)
diff --git a/mobile/touches_ios.go b/mobile/touches_ios.go
index 3f0afaa3a..b644dd8de 100644
--- a/mobile/touches_ios.go
+++ b/mobile/touches_ios.go
@@ -16,6 +16,10 @@
 
 package mobile
 
+import (
+	"fmt"
+)
+
 // #cgo CFLAGS: -x objective-c
 // #cgo LDFLAGS: -framework Foundation -framework UIKit
 //
@@ -55,6 +59,6 @@ func updateTouchesOnIOSImpl(phase int, ptr int64, x, y int) {
 		delete(touches, id)
 		updateTouches()
 	default:
-		panic("not reached")
+		panic(fmt.Sprintf("mobile: invalid phase: %d", phase))
 	}
 }