add export layers, export png, import brush padding

src/image.cpp

@@ -59,6 +59,18 @@ void Image::flip()
     std::swap(m_data, flipped);
 }
 
+void Image::gayscale_alpha()
+{
+    int np = width * height;
+    auto ptr = reinterpret_cast<glm::u8vec4*>(m_data.get());
+    for (int i = 0; i < np; i++)
+    {
+        auto& c = ptr[i];
+        c.g = c.b = c.r = 255 - c.a;
+        c.a = 255;
+    }
+}
+
 Image Image::resize(int w, int h) const
 {
     Image ret;
@@ -90,3 +102,50 @@ Image Image::resize(int w, int h) const
     }
     return ret;
 }
+
+Image Image::resize_power2() const
+{
+    int w = pow(2, ceil(log(width) / log(2)));
+    int h = pow(2, ceil(log(height) / log(2)));
+    if (w == width && h == height)
+    {
+        Image i;
+        i.create(width, height);
+        std::copy(m_data.get(), m_data.get() + width * height * comp, i.m_data.get());
+        return i;
+    }
+    return resize(w, h);
+}
+
+Image Image::resize_squared() const
+{
+    Image ret;
+    if (width == height)
+    {
+        ret.create(width, height);
+        std::copy(m_data.get(), m_data.get() + width * height * comp, ret.m_data.get());
+    }
+    else
+    {
+        int pad_x = 0;
+        int pad_y = 0;
+        int size = 0;
+        if (height > width)
+        {
+            size = height;
+            pad_x = (size - width) / 2;
+        }
+        else
+        {
+            size = width;
+            pad_y = (size - height) / 2;
+        }
+        ret.create(size, size);
+        auto ptr_src = reinterpret_cast<glm::u8vec4*>(m_data.get());
+        auto ptr_dst = reinterpret_cast<glm::u8vec4*>(ret.m_data.get());
+        std::fill_n(ptr_dst, size * size, glm::u8vec4(0));
+        for (int y = 0; y < height; y++)
+            std::copy_n(ptr_src + y * width, width, ptr_dst + pad_x + (y + pad_y) * ret.width);
+    }
+    return ret;
+}