graphics: Add comments

image.go

@@ -281,6 +281,7 @@ func newImageWithScreenFramebuffer(width, height int, offsetX, offsetY float64)
 	return i
 }
 
+// MaxImageSize represents the maximum width/height of an image.
 const MaxImageSize = restorable.MaxImageSize
 
 func checkSize(width, height int) {

internal/graphics/command.go

@@ -37,6 +37,7 @@ type command interface {
 	Exec(indexOffsetInBytes int) error
 }
 
+// commandQueue is a command queue for drawing commands.
 type commandQueue struct {
 	commands    []command
 	vertices    []float32
@@ -44,6 +45,7 @@ type commandQueue struct {
 	m           sync.Mutex
 }
 
+// theCommandQueue is the command queue for the current process.
 var theCommandQueue = &commandQueue{}
 
 func (q *commandQueue) appendVertices(vertices []float32) {