Fixes fit resizing smaller images and adds comments about broken scaling

examples/test-pattern.ppm

@@ -0,0 +1,5 @@
+P3 6 4 1  
+1 0 0 1 0 0   0 1 0 0 1 0   0 0 1 0 0 1
+1 1 0 1 1 0   1 1 1 1 1 1   0 0 0 0 0 0
+1 1 0 1 1 0   1 1 1 1 1 1   0 0 0 0 0 0
+1 0 0 1 0 0   0 1 0 0 1 0   0 0 1 0 0 1

main.go

@@ -152,6 +152,9 @@ func (i *image) BuildCells(bm []int) {
 	}
 }
 
+// TODO this works for shrinking mostly, but blowing up is broken
+// particularly for small images. This is due to rows being combined
+// in pairs. Maybe this processing can happen elsewhere?
 func (i *image) ScaleColor(newWidth int) {
 	newHeight := int(float64(newWidth) * (float64(i.height) / float64(i.width))) / 2
 
@@ -173,6 +176,9 @@ func (i *image) ScaleColor(newWidth int) {
 	i.colorImage = out
 }
 
+// TODO this works for shrinking mostly, but blowing up is broken
+// particularly for small images. This is due to rows being combined
+// in pairs. Maybe this processing can happen elsewhere?
 func (i *image) Scale(newWidth int) {
 	newHeight := int(float64(newWidth) * (float64(i.height) / float64(i.width))) / 2
 
@@ -293,19 +299,23 @@ func main() {
 	if err != nil {
 		HandleError(err)
 	}
-	if *fitToWidth || *scaleToWidth != -1 {
-		cols, _ := termios.GetWindowSize()
+	cols := -1
+	if *fitToWidth {
+		cols, _ = termios.GetWindowSize()
 		if img.width < cols {
-			cols = img.width
-		}
-		if *scaleToWidth != -1 {
-			cols = *scaleToWidth
+			cols = -1
 		}
+	} else if *scaleToWidth != -1 {
+		cols = *scaleToWidth
+	}
+
+	if cols != -1 {
 		if img.pbmType == "P3" {
 			img.ScaleColor(cols)
 		} else {
 			img.Scale(cols)
 		}
 	}
+
 	fmt.Print(img.String())
 }