internal/graphicsdriver: let some functions return an error

This is a preparation for the DirectX driver.

Updates #1007

internal/graphicscommand/command.go

@@ -279,7 +279,9 @@ func (q *commandQueue) flush(graphicsDriver graphicsdriver.Graphics) error {
 		}
 	}
 
-	graphicsDriver.Begin()
+	if err := graphicsDriver.Begin(); err != nil {
+		return err
+	}
 	var present bool
 	cs := q.commands
 	for len(cs) > 0 {
@@ -303,7 +305,9 @@ func (q *commandQueue) flush(graphicsDriver graphicsdriver.Graphics) error {
 			nc++
 		}
 		if 0 < ne {
-			graphicsDriver.SetVertices(vs[:nv], es[:ne])
+			if err := graphicsDriver.SetVertices(vs[:nv], es[:ne]); err != nil {
+				return err
+			}
 			es = es[ne:]
 			vs = vs[nv:]
 		}
@@ -322,7 +326,9 @@ func (q *commandQueue) flush(graphicsDriver graphicsdriver.Graphics) error {
 		}
 		cs = cs[nc:]
 	}
-	graphicsDriver.End(present)
+	if err := graphicsDriver.End(present); err != nil {
+		return err
+	}
 
 	// Release the commands explicitly (#1803).
 	// Apparently, the part of a slice between len and cap-1 still holds references.
@@ -611,7 +617,9 @@ func (c *replacePixelsCommand) Exec(graphicsDriver graphicsdriver.Graphics, inde
 	}
 
 	if len(c.args[lastArgIdx:]) > 0 {
-		c.dst.image.ReplacePixels(c.args[lastArgIdx:])
+		if err := c.dst.image.ReplacePixels(c.args[lastArgIdx:]); err != nil {
+			return err
+		}
 	}
 	return nil
 }

internal/graphicsdriver/graphics.go

@@ -41,10 +41,10 @@ type ColorM interface {
 
 type Graphics interface {
 	Initialize() error
-	Begin()
-	End(present bool)
+	Begin() error
+	End(present bool) error
 	SetTransparent(transparent bool)
-	SetVertices(vertices []float32, indices []uint16)
+	SetVertices(vertices []float32, indices []uint16) error
 	NewImage(width, height int) (Image, error)
 	NewScreenFramebufferImage(width, height int) (Image, error)
 	SetVsyncEnabled(enabled bool)
@@ -76,7 +76,7 @@ type Image interface {
 	Dispose()
 	IsInvalidated() bool
 	ReadPixels(buf []byte) error
-	ReplacePixels(args []*ReplacePixelsArgs)
+	ReplacePixels(args []*ReplacePixelsArgs) error
 }
 
 type ImageID int

internal/graphicsdriver/metal/graphics_darwin.go

@@ -363,17 +363,19 @@ func Get() *Graphics {
 	return &theGraphics
 }
 
-func (g *Graphics) Begin() {
+func (g *Graphics) Begin() error {
 	// NSAutoreleasePool is required to release drawable correctly (#847).
 	// https://developer.apple.com/library/archive/documentation/3DDrawing/Conceptual/MTLBestPracticesGuide/Drawables.html
 	g.pool = C.allocAutoreleasePool()
+	return nil
 }
 
-func (g *Graphics) End(present bool) {
+func (g *Graphics) End(present bool) error {
 	g.flushIfNeeded(present)
 	g.screenDrawable = ca.MetalDrawable{}
 	C.releaseAutoreleasePool(g.pool)
 	g.pool = nil
+	return nil
 }
 
 func (g *Graphics) SetWindow(window uintptr) {
@@ -457,7 +459,7 @@ func (g *Graphics) availableBuffer(length uintptr) mtl.Buffer {
 	return newBuf
 }
 
-func (g *Graphics) SetVertices(vertices []float32, indices []uint16) {
+func (g *Graphics) SetVertices(vertices []float32, indices []uint16) error {
 	vbSize := unsafe.Sizeof(vertices[0]) * uintptr(len(vertices))
 	ibSize := unsafe.Sizeof(indices[0]) * uintptr(len(indices))
 
@@ -466,6 +468,8 @@ func (g *Graphics) SetVertices(vertices []float32, indices []uint16) {
 
 	g.ib = g.availableBuffer(ibSize)
 	g.ib.CopyToContents(unsafe.Pointer(&indices[0]), ibSize)
+
+	return nil
 }
 
 func (g *Graphics) flushIfNeeded(present bool) {
@@ -1166,7 +1170,7 @@ func (i *Image) ReadPixels(buf []byte) error {
 	return nil
 }
 
-func (i *Image) ReplacePixels(args []*graphicsdriver.ReplacePixelsArgs) {
+func (i *Image) ReplacePixels(args []*graphicsdriver.ReplacePixelsArgs) error {
 	g := i.graphics
 
 	g.flushRenderCommandEncoderIfNeeded()
@@ -1226,6 +1230,8 @@ func (i *Image) ReplacePixels(args []*graphicsdriver.ReplacePixelsArgs) {
 		bce.CopyFromTexture(t, 0, 0, so, ss, i.texture, 0, 0, do)
 	}
 	bce.EndEncoding()
+
+	return nil
 }
 
 func (i *Image) mtlTexture() mtl.Texture {

internal/graphicsdriver/opengl/graphics.go

@@ -56,14 +56,16 @@ type Graphics struct {
 	activatedTextures []activatedTexture
 }
 
-func (g *Graphics) Begin() {
+func (g *Graphics) Begin() error {
 	// Do nothing.
+	return nil
 }
 
-func (g *Graphics) End(present bool) {
+func (g *Graphics) End(present bool) error {
 	// Call glFlush to prevent black flicking (especially on Android (#226) and iOS).
 	// TODO: examples/sprites worked without this. Is this really needed?
 	g.context.flush()
+	return nil
 }
 
 func (g *Graphics) SetTransparent(transparent bool) {
@@ -151,12 +153,13 @@ func (g *Graphics) Reset() error {
 	return g.state.reset(&g.context)
 }
 
-func (g *Graphics) SetVertices(vertices []float32, indices []uint16) {
+func (g *Graphics) SetVertices(vertices []float32, indices []uint16) error {
 	// Note that the vertices passed to BufferSubData is not under GC management
 	// in opengl package due to unsafe-way.
 	// See BufferSubData in context_mobile.go.
 	g.context.arrayBufferSubData(vertices)
 	g.context.elementArrayBufferSubData(indices)
+	return nil
 }
 
 func (g *Graphics) uniformVariableName(idx int) string {

internal/graphicsdriver/opengl/image.go

@@ -15,6 +15,8 @@
 package opengl
 
 import (
+	"errors"
+
 	"github.com/hajimehoshi/ebiten/v2/internal/graphics"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
 )
@@ -118,12 +120,12 @@ func (i *Image) ensureStencilBuffer() error {
 	return nil
 }
 
-func (i *Image) ReplacePixels(args []*graphicsdriver.ReplacePixelsArgs) {
+func (i *Image) ReplacePixels(args []*graphicsdriver.ReplacePixelsArgs) error {
 	if i.screen {
-		panic("opengl: ReplacePixels cannot be called on the screen, that doesn't have a texture")
+		return errors.New("opengl: ReplacePixels cannot be called on the screen")
 	}
 	if len(args) == 0 {
-		return
+		return nil
 	}
 
 	// glFlush is necessary on Android.
@@ -133,4 +135,5 @@ func (i *Image) ReplacePixels(args []*graphicsdriver.ReplacePixelsArgs) {
 	}
 	i.graphics.drawCalled = false
 	i.graphics.context.texSubImage2D(i.texture, args)
+	return nil
 }