Only use the transparent image generation if there where any transparent blocks.

common/renderer.go

@@ -166,7 +166,8 @@ func (r *Renderer) Reset() {
 		r.yMin[i] = math.MinInt32
 	}
 
-	if r.tBuffer != nil {
+	if r.TransparentBlocks > 0 {
+		r.TransparentBlocks = 0
 		for i, t := range r.tBuffer {
 			if t != nil {
 				r.spans.FreeAll(t)
@@ -174,6 +175,8 @@ func (r *Renderer) Reset() {
 			}
 		}
 	}
+	r.SolidBlocks = 0
+	r.RejectedBlocks = 0
 }
 
 func (r *Renderer) IsFilled() bool {
@@ -416,7 +419,7 @@ func (r *Renderer) CreateShadedImage(
 
 	pix := image.Pix
 
-	if r.tBuffer != nil { // Fast path for transparent images.
+	if r.TransparentBlocks > 0 { // Fast path for transparent images.
 		for z := height - 1; z >= 0; z-- {
 			for x := 0; x < width; x++ {
 				colIdx := r.cBuffer[ofs]