diff --git a/imageparts.go b/imageparts.go
index 25ae3b09d..81e80befa 100644
--- a/imageparts.go
+++ b/imageparts.go
@@ -84,8 +84,9 @@ type textureQuads struct {
 }
 
 func (t *textureQuads) vertices() []uint8 {
+	const size = graphics.QuadVertexNum
 	l := t.parts.Len()
-	vertices := make([]uint8, l*32)
+	vertices := make([]uint8, l*size)
 	p := t.parts
 	w, h := t.width, t.height
 	width2p := int(graphics.NextPowerOf2Int32(int32(w)))
@@ -104,73 +105,73 @@ func (t *textureQuads) vertices() []uint8 {
 		u0, v0, u1, v1 := u(sx0, width2p), v(sy0, height2p), u(sx1, width2p), v(sy1, height2p)
 		// Use direct assign here. `append` function might be slow on browsers.
 		if endian.IsLittle() {
-			vertices[32*n] = uint8(x0)
-			vertices[32*n+1] = uint8(x0 >> 8)
-			vertices[32*n+2] = uint8(y0)
-			vertices[32*n+3] = uint8(y0 >> 8)
-			vertices[32*n+4] = uint8(u0)
-			vertices[32*n+5] = uint8(u0 >> 8)
-			vertices[32*n+6] = uint8(v0)
-			vertices[32*n+7] = uint8(v0 >> 8)
-			vertices[32*n+8] = uint8(x1)
-			vertices[32*n+9] = uint8(x1 >> 8)
-			vertices[32*n+10] = uint8(y0)
-			vertices[32*n+11] = uint8(y0 >> 8)
-			vertices[32*n+12] = uint8(u1)
-			vertices[32*n+13] = uint8(u1 >> 8)
-			vertices[32*n+14] = uint8(v0)
-			vertices[32*n+15] = uint8(v0 >> 8)
-			vertices[32*n+16] = uint8(x0)
-			vertices[32*n+17] = uint8(x0 >> 8)
-			vertices[32*n+18] = uint8(y1)
-			vertices[32*n+19] = uint8(y1 >> 8)
-			vertices[32*n+20] = uint8(u0)
-			vertices[32*n+21] = uint8(u0 >> 8)
-			vertices[32*n+22] = uint8(v1)
-			vertices[32*n+23] = uint8(v1 >> 8)
-			vertices[32*n+24] = uint8(x1)
-			vertices[32*n+25] = uint8(x1 >> 8)
-			vertices[32*n+26] = uint8(y1)
-			vertices[32*n+27] = uint8(y1 >> 8)
-			vertices[32*n+28] = uint8(u1)
-			vertices[32*n+29] = uint8(u1 >> 8)
-			vertices[32*n+30] = uint8(v1)
-			vertices[32*n+31] = uint8(v1 >> 8)
+			vertices[size*n] = uint8(x0)
+			vertices[size*n+1] = uint8(x0 >> 8)
+			vertices[size*n+2] = uint8(y0)
+			vertices[size*n+3] = uint8(y0 >> 8)
+			vertices[size*n+4] = uint8(u0)
+			vertices[size*n+5] = uint8(u0 >> 8)
+			vertices[size*n+6] = uint8(v0)
+			vertices[size*n+7] = uint8(v0 >> 8)
+			vertices[size*n+8] = uint8(x1)
+			vertices[size*n+9] = uint8(x1 >> 8)
+			vertices[size*n+10] = uint8(y0)
+			vertices[size*n+11] = uint8(y0 >> 8)
+			vertices[size*n+12] = uint8(u1)
+			vertices[size*n+13] = uint8(u1 >> 8)
+			vertices[size*n+14] = uint8(v0)
+			vertices[size*n+15] = uint8(v0 >> 8)
+			vertices[size*n+16] = uint8(x0)
+			vertices[size*n+17] = uint8(x0 >> 8)
+			vertices[size*n+18] = uint8(y1)
+			vertices[size*n+19] = uint8(y1 >> 8)
+			vertices[size*n+20] = uint8(u0)
+			vertices[size*n+21] = uint8(u0 >> 8)
+			vertices[size*n+22] = uint8(v1)
+			vertices[size*n+23] = uint8(v1 >> 8)
+			vertices[size*n+24] = uint8(x1)
+			vertices[size*n+25] = uint8(x1 >> 8)
+			vertices[size*n+26] = uint8(y1)
+			vertices[size*n+27] = uint8(y1 >> 8)
+			vertices[size*n+28] = uint8(u1)
+			vertices[size*n+29] = uint8(u1 >> 8)
+			vertices[size*n+30] = uint8(v1)
+			vertices[size*n+31] = uint8(v1 >> 8)
 		} else {
-			vertices[32*n] = uint8(x0 >> 8)
-			vertices[32*n+1] = uint8(x0)
-			vertices[32*n+2] = uint8(y0 >> 8)
-			vertices[32*n+3] = uint8(y0)
-			vertices[32*n+4] = uint8(u0 >> 8)
-			vertices[32*n+5] = uint8(u0)
-			vertices[32*n+6] = uint8(v0 >> 8)
-			vertices[32*n+7] = uint8(v0)
-			vertices[32*n+8] = uint8(x1 >> 8)
-			vertices[32*n+9] = uint8(x1)
-			vertices[32*n+10] = uint8(y0 >> 8)
-			vertices[32*n+11] = uint8(y0)
-			vertices[32*n+12] = uint8(u1 >> 8)
-			vertices[32*n+13] = uint8(u1)
-			vertices[32*n+14] = uint8(v0 >> 8)
-			vertices[32*n+15] = uint8(v0)
-			vertices[32*n+16] = uint8(x0 >> 8)
-			vertices[32*n+17] = uint8(x0)
-			vertices[32*n+18] = uint8(y1 >> 8)
-			vertices[32*n+19] = uint8(y1)
-			vertices[32*n+20] = uint8(u0 >> 8)
-			vertices[32*n+21] = uint8(u0)
-			vertices[32*n+22] = uint8(v1 >> 8)
-			vertices[32*n+23] = uint8(v1)
-			vertices[32*n+24] = uint8(x1 >> 8)
-			vertices[32*n+25] = uint8(x1)
-			vertices[32*n+26] = uint8(y1 >> 8)
-			vertices[32*n+27] = uint8(y1)
-			vertices[32*n+28] = uint8(u1 >> 8)
-			vertices[32*n+29] = uint8(u1)
-			vertices[32*n+30] = uint8(v1 >> 8)
-			vertices[32*n+31] = uint8(v1)
+			vertices[size*n] = uint8(x0 >> 8)
+			vertices[size*n+1] = uint8(x0)
+			vertices[size*n+2] = uint8(y0 >> 8)
+			vertices[size*n+3] = uint8(y0)
+			vertices[size*n+4] = uint8(u0 >> 8)
+			vertices[size*n+5] = uint8(u0)
+			vertices[size*n+6] = uint8(v0 >> 8)
+			vertices[size*n+7] = uint8(v0)
+			vertices[size*n+8] = uint8(x1 >> 8)
+			vertices[size*n+9] = uint8(x1)
+			vertices[size*n+10] = uint8(y0 >> 8)
+			vertices[size*n+11] = uint8(y0)
+			vertices[size*n+12] = uint8(u1 >> 8)
+			vertices[size*n+13] = uint8(u1)
+			vertices[size*n+14] = uint8(v0 >> 8)
+			vertices[size*n+15] = uint8(v0)
+			vertices[size*n+16] = uint8(x0 >> 8)
+			vertices[size*n+17] = uint8(x0)
+			vertices[size*n+18] = uint8(y1 >> 8)
+			vertices[size*n+19] = uint8(y1)
+			vertices[size*n+20] = uint8(u0 >> 8)
+			vertices[size*n+21] = uint8(u0)
+			vertices[size*n+22] = uint8(v1 >> 8)
+			vertices[size*n+23] = uint8(v1)
+			vertices[size*n+24] = uint8(x1 >> 8)
+			vertices[size*n+25] = uint8(x1)
+			vertices[size*n+26] = uint8(y1 >> 8)
+			vertices[size*n+27] = uint8(y1)
+			vertices[size*n+28] = uint8(u1 >> 8)
+			vertices[size*n+29] = uint8(u1)
+			vertices[size*n+30] = uint8(v1 >> 8)
+			vertices[size*n+31] = uint8(v1)
 		}
 		n++
 	}
-	return vertices[:n*32]
+	return vertices[:n*size]
 }
diff --git a/internal/graphics/command.go b/internal/graphics/command.go
index 957815a55..8e3e06c46 100644
--- a/internal/graphics/command.go
+++ b/internal/graphics/command.go
@@ -108,8 +108,8 @@ func (q *commandQueue) Flush(context *opengl.Context) error {
 		}
 		// NOTE: WebGL doesn't seem to have Check gl.MAX_ELEMENTS_VERTICES or gl.MAX_ELEMENTS_INDICES so far.
 		// Let's use them to compare to len(quads) in the future.
-		if maxQuads < len(vertices)/quadVertexNum {
-			return errors.New(fmt.Sprintf("len(quads) must be equal to or less than %d", maxQuads))
+		if maxQuads < len(vertices)/QuadVertexNum {
+			return fmt.Errorf("len(quads) must be equal to or less than %d", maxQuads)
 		}
 		numc := len(g)
 		indexOffsetInBytes := 0
@@ -118,7 +118,7 @@ func (q *commandQueue) Flush(context *opengl.Context) error {
 				return err
 			}
 			if c, ok := c.(*drawImageCommand); ok {
-				indexOffsetInBytes += 6 * len(c.vertices) / quadVertexNum * 2
+				indexOffsetInBytes += 6 * len(c.vertices) / QuadVertexNum * 2
 			}
 		}
 		if 0 < numc {
@@ -162,7 +162,7 @@ type drawImageCommand struct {
 }
 
 const (
-	quadVertexNum = 32 // 4 * 2 [vertices] * 2 [tex_coords] * 2[bytes]
+	QuadVertexNum = 32 // 4 * 2 [vertices] * 2 [tex_coords] * 2[bytes]
 )
 
 func (c *drawImageCommand) Exec(context *opengl.Context, indexOffsetInBytes int) error {
@@ -199,13 +199,13 @@ func (c *drawImageCommand) Exec(context *opengl.Context, indexOffsetInBytes int)
 func (c *drawImageCommand) split(quadsNum int) [2]*drawImageCommand {
 	c1 := *c
 	c2 := *c
-	c1.vertices = c.vertices[:quadsNum*quadVertexNum]
-	c2.vertices = c.vertices[quadsNum*quadVertexNum:]
+	c1.vertices = c.vertices[:quadsNum*QuadVertexNum]
+	c2.vertices = c.vertices[quadsNum*QuadVertexNum:]
 	return [2]*drawImageCommand{&c1, &c2}
 }
 
 func (c *drawImageCommand) quadsNum() int {
-	return len(c.vertices) / quadVertexNum
+	return len(c.vertices) / QuadVertexNum
 }
 
 type replacePixelsCommand struct {