Updated Tutorial:Screen, colors and squares (markdown)

Tutorial:Screen,-colors-and-squares.md

@@ -15,13 +15,16 @@ import (
 func update(screen *ebiten.Image) error {
     // Display the text though the debug function
     if err := ebitenutil.DebugPrint(screen, "Our first game in Ebiten!"); err != nil {
+        return err
     }
     return nil
 }
 
 func main() {
     // Initialize Ebiten, and loop the update() function
-    ebiten.Run(update, 320, 240, 2, "Hello world!")
+    if err := ebiten.Run(update, 320, 240, 2, "Hello world!"); err != nil {
+        panic(err)
+    }
 }
 ```
 
@@ -39,9 +42,10 @@ You will need to import the `image/color` package to create the color struct by
 
 ```go
 import (
+    "image/color"
+
     "github.com/hajimehoshi/ebiten"
     "github.com/hajimehoshi/ebiten/ebitenutil"
-    "image/color"
 )
 ```
 
@@ -63,10 +67,14 @@ Remember the `update()` function? Yeah, the function which keeps being called by
 func update(screen *ebiten.Image) error {
     
     // Fill the screen with #FF0000 color
-    screen.Fill(color.NRGBA{0xff, 0x00, 0x00, 0xff})
+    if err := screen.Fill(color.NRGBA{0xff, 0x00, 0x00, 0xff}); err != nil {
+        return err
+    }
     
     // Display the text though the debug function
-    ebitenutil.DebugPrint(screen, "Our first game in Ebiten!")
+    if err := ebitenutil.DebugPrint(screen, "Our first game in Ebiten!"); err != nil {
+        return err
+    }
     
     return nil
 }
@@ -115,25 +123,41 @@ You will need to render the new image to the main screen once you've created it,
 Here's the fully example, we'll explain it later. The examples above were be done in the `update()` function, so let's see what should your `update()` function be this time.
 
 ```go
+var square *ebiten.Image
+
+func init() {
+    // Create an 16x16 image
+    var err error
+    square, err = ebiten.NewImage(16, 16, ebiten.FilterNearest)
+    if err != nil {
+        panic(err)
+    }
+}
+
 func update(screen *ebiten.Image) error {
     
     // Fill the screen with #FF0000 color
-    screen.Fill(color.NRGBA{0xff, 0x00, 0x00, 0xff})
+    if err := screen.Fill(color.NRGBA{0xff, 0x00, 0x00, 0xff}); err != nil {
+        return err
+    }
     
     // Display the text though the debug function
-    ebitenutil.DebugPrint(screen, "Our first game in Ebiten!")
+    if err := ebitenutil.DebugPrint(screen, "Our first game in Ebiten!"); err != nil {
-
+        return err
-    // Create an 16x16 image
+    }
-    square, _ := ebiten.NewImage(16, 16, ebiten.FilterNearest)
 
     // Fill the square with the white color
-    square.Fill(color.White)
+    if err := square.Fill(color.White); err != nil {
+        return err
+    }
 
     // Create an empty option struct
     opts := &ebiten.DrawImageOptions{}
     
     // Draw the square image to the screen with an empty option
-    screen.DrawImage(square, opts)
+    if err := screen.DrawImage(square, opts); err != nil {
+        return err
+    }
     
     return nil
 }