implement pen and erase as strategy pattern introducing the CanvasMode classes

engine/canvas.cpp

@@ -3,6 +3,10 @@
 #include "canvas.h"
 
 ui::Canvas* ui::Canvas::I;
+CanvasMode* ui::Canvas::modes[] = {
+    new CanvasModePen,
+    new CanvasModePen,
+};
 glm::vec3 ui::Canvas::m_plane_origin[6] = {
     { 0, 0,-1}, // front
     { 1, 0, 0}, // right
@@ -88,7 +92,7 @@ void ui::Canvas::stroke_draw()
         else
         {
             glDisable(GL_BLEND);
-            if (m_state == kPenState::Erase)
+            if (m_state == kCanvasMode::Erase)
             {
                 ShaderManager::use(ui::kShader::StrokeErase);
                 //ShaderManager::u_vec4(kShaderUniform::Col, m_brush.m_tip_color);
@@ -275,7 +279,7 @@ void ui::Canvas::stroke_commit()
         m_tex2[i].bind();
         m_sampler.bind(0);
         m_sampler_bg.bind(1);
-        if (m_state == kPenState::Erase)
+        if (m_state == kCanvasMode::Erase)
         {
             ShaderManager::use(ui::kShader::Texture);
         }
@@ -324,7 +328,7 @@ void ui::Canvas::stroke_start(glm::vec2 point, float pressure, const ui::Brush&
         m_dirty_box[i] = glm::vec4(m_width, m_height, 0, 0); // reset bounding box
         m_dirty_face[i] = false;
         
-        if (m_state == kPenState::Erase)
+        if (m_state == kCanvasMode::Erase)
         {
             m_layers[m_current_layer_idx].m_rtt[i].bindFramebuffer();
             m_tmp[i].bindTexture();