add support for high res brush textures, implement mipmaps on brush

engine/canvas.cpp

@@ -196,7 +196,7 @@ void ui::Canvas::stroke_draw()
     auto samples = m_current_stroke->compute_samples();
     auto& tex = TextureManager::get(m_brush.m_tex_id);
     tex.bind();
-    m_sampler.bind(0);
+    m_sampler_brush.bind(0);
     m_sampler_bg.bind(1);
     m_sampler_mask.bind(2);
 
@@ -233,7 +233,7 @@ void ui::Canvas::stroke_draw()
             ShaderManager::u_vec2(kShaderUniform::Resolution, { m_width, m_height });
             for (const auto& s : samples)
             {
-                glm::vec2 dx(s.size, 0), dy(0, s.size);
+                glm::vec2 dx(s.size * 0.5f, 0), dy(0, s.size * 0.5f);
                 glm::vec2 off[4] = {
                     - dx - dy, // A - bottom-left
                     - dx + dy, // B - top-left
@@ -317,7 +317,7 @@ void ui::Canvas::stroke_draw()
     glDisable(GL_BLEND);
 
     glActiveTexture(GL_TEXTURE0);
-    m_sampler.unbind();
+    m_sampler_brush.unbind();
     m_sampler_bg.unbind();
     m_sampler_mask.unbind();
     tex.unbind();
@@ -695,6 +695,8 @@ bool ui::Canvas::create(int width, int height)
         m_tex2[i].create(width, height); // TODO: destroy before recreating
     }
     m_sampler.create(GL_NEAREST);
+    m_sampler_brush.create();
+    m_sampler_brush.set_filter(GL_LINEAR_MIPMAP_LINEAR, GL_LINEAR);
     m_sampler_bg.create(GL_NEAREST);
     m_sampler_mask.create(GL_NEAREST);
     m_plane.create<1>(1, 1);