use NUM2DBL() instead of RFLOAT_VALUE()

src/GL.cc

@@ -30,10 +30,10 @@ static VALUE GL_draw_rect(VALUE klass,
     glUniform2i(programs[PROGRAM_RECT]->uniforms[UNIFORM_POSITION], FIX2INT(x), FIX2INT(y));
     glUniform2i(programs[PROGRAM_RECT]->uniforms[UNIFORM_SIZE], FIX2INT(width), FIX2INT(height));
     glUniform4f(programs[PROGRAM_RECT]->uniforms[UNIFORM_COLOR],
-                RFLOAT_VALUE(r),
-                RFLOAT_VALUE(g),
-                RFLOAT_VALUE(b),
-                RFLOAT_VALUE(a));
+                NUM2DBL(r),
+                NUM2DBL(g),
+                NUM2DBL(b),
+                NUM2DBL(a));
     rect_buffer->bind();
     glEnableVertexAttribArray(0);
     glVertexAttribIPointer(0, 2, GL_INT, 0, 0);