DrawImage can now take image.Image values; added error messages if the automatic image and font loading doesn't work

canvas.go

@@ -4,6 +4,7 @@ package canvas
 
 import (
 	"fmt"
+	"os"
 
 	"github.com/golang/freetype/truetype"
 )
@@ -407,13 +408,16 @@ func parseStyle(value ...interface{}) drawStyle {
 		case *RadialGradient:
 			style.radialGradient = v
 			return style
-		case *Image, string:
-			style.image = getImage(v)
 		}
 	}
 	c, ok := parseColor(value...)
 	if ok {
 		style.color = c
+	} else if len(value) == 1 {
+		switch v := value[0].(type) {
+		case *Image, string:
+			style.image = getImage(v)
+		}
 	}
 	return style
 }
@@ -625,11 +629,11 @@ func (cv *Canvas) SetLineWidth(width float64) {
 // SetFont sets the font and font size. The font parameter can be a font loaded
 // with the LoadFont function, a filename for a font to load (which will be
 // cached), or nil, in which case the first loaded font will be used
-func (cv *Canvas) SetFont(font interface{}, size float64) {
+func (cv *Canvas) SetFont(src interface{}, size float64) {
-	if font == nil {
+	if src == nil {
 		cv.state.font = defaultFont
 	} else {
-		switch v := font.(type) {
+		switch v := src.(type) {
 		case *Font:
 			cv.state.font = v
 		case *truetype.Font:
@@ -639,7 +643,10 @@ func (cv *Canvas) SetFont(font interface{}, size float64) {
 				cv.state.font = f
 			} else {
 				f, err := LoadFont(v)
-				if err == nil {
+				if err != nil {
+					fmt.Fprintf(os.Stderr, "Error loading font %s: %v\n", v, err)
+					fonts[v] = nil
+				} else {
 					fonts[v] = f
 					cv.state.font = f
 				}

images.go

@@ -3,9 +3,12 @@ package canvas
 import (
 	"bytes"
 	"errors"
+	"fmt"
 	"image"
 	"io/ioutil"
+	"os"
 	"runtime"
+	"strings"
 	"unsafe"
 )
 
@@ -17,7 +20,7 @@ type Image struct {
 	opaque  bool
 }
 
-var images = make(map[string]*Image)
+var images = make(map[interface{}]*Image)
 
 // LoadImage loads an image. The src parameter can be either an image from the
 // standard image package, a byte slice that will be loaded, or a file name
@@ -74,21 +77,38 @@ func LoadImage(src interface{}) (*Image, error) {
 	return img, nil
 }
 
-func getImage(image interface{}) *Image {
+func getImage(src interface{}) *Image {
-	switch v := image.(type) {
+	if img, ok := images[src]; ok {
-	case *Image:
-		return v
-	case string:
-		if img, ok := images[v]; ok {
 		return img
 	}
+	switch v := src.(type) {
+	case *Image:
+		return v
+	case image.Image:
 		img, err := LoadImage(v)
 		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error loading image: %v\n", err)
+			images[src] = nil
+			return nil
+		}
+		images[v] = img
+		return img
+	case string:
+		img, err := LoadImage(v)
+		if err != nil {
+			if strings.Contains(strings.ToLower(err.Error()), "format") {
+				fmt.Fprintf(os.Stderr, "Error loading image %s: %v\nIt may be necessary to import the appropriate decoder, e.g.\nimport _ \"image/jpeg\"\n", v, err)
+			} else {
+				fmt.Fprintf(os.Stderr, "Error loading image %s: %v\n", v, err)
+			}
+			images[src] = nil
 			return nil
 		}
 		images[v] = img
 		return img
 	}
+	fmt.Fprintf(os.Stderr, "Unknown image type: %T\n", src)
+	images[src] = nil
 	return nil
 }