add checkerboard shader and draw it

engine/app.cpp

@@ -240,6 +240,28 @@ void App::initShaders()
         "   frag = vec4(rgb, alpha_tot);\n"
         "}\n";
 
+    static const char* shader_checkerboard_v =
+        SHADER_VERSION
+        "uniform mat4 mvp;\n"
+        "in vec4 pos;\n"
+        "in vec2 uvs;\n"
+        "out vec2 uv;\n"
+        "void main(){\n"
+        "   uv = uvs;\n"
+        "   gl_Position = mvp * vec4(pos.xyz, 1.0);\n"
+        "}";
+    static const char* shader_checkerboard_f =
+        SHADER_VERSION
+        "in mediump vec2 uv;\n"
+        "out mediump vec4 frag;\n"
+        "void main(){\n"
+        "   const vec4 c1 = vec4(1.0, 1.0, 1.0, 1.0);\n"
+        "   const vec4 c2 = vec4(0.9, 0.9, 0.9, 1.0);\n"
+        "   vec2 c = floor(fract(uv * 10.0) * 2.0);\n"
+        "   float alpha = mix(c.x, 1.0 - c.x, c.y);\n"
+        "   frag = mix(c1, c2, alpha);\n"
+        "}";
+
     LOG("initializing shaders");
     if (!ShaderManager::create(kShader::Texture, shader_v, shader_f))
         LOG("Failed to create shader Texture");
@@ -263,6 +285,8 @@ void App::initShaders()
         LOG("Failed to create shader StrokeErase");
     if (!ShaderManager::create(kShader::StrokeLayer, shader_stroke_layer_v, shader_stroke_layer_f))
         LOG("Failed to create shader StrokeLayer");
+    if (!ShaderManager::create(kShader::Checkerboard, shader_checkerboard_v, shader_checkerboard_f))
+        LOG("Failed to create shader Checkerboard");
     LOG("shaders initialized");
 }
 

engine/layout.h

@@ -1932,19 +1932,24 @@ public:
 //         auto plane_mvp = proj * camera * transform *
 //             glm::scale(glm::vec3(sz, 1));
 
+
         m_sampler.bind(0);
-        ui::ShaderManager::use(kShader::TextureAlpha);
-        ui::ShaderManager::u_int(kShaderUniform::Tex, 0);
-        
         auto blend = glIsEnabled(GL_BLEND);
         
         glEnable(GL_BLEND);
-        for (auto layer_index : m_canvas->m_order)
+        for (int plane_index = 0; plane_index < 6; plane_index++)
         {
-            for (int plane_index = 0; plane_index < 6; plane_index++)
+            auto plane_mvp = proj * camera * m_canvas->m_plane_transform[plane_index] * glm::translate(glm::vec3(0, 0, -1));
+
+            ui::ShaderManager::use(kShader::Checkerboard);
+            ui::ShaderManager::u_mat4(kShaderUniform::MVP, plane_mvp);
+            m_face_plane.draw_fill();
+
+            ui::ShaderManager::use(kShader::TextureAlpha);
+            ui::ShaderManager::u_int(kShaderUniform::Tex, 0);
+            ui::ShaderManager::u_mat4(kShaderUniform::MVP, plane_mvp);
+            for (auto layer_index : m_canvas->m_order)
             {
-                auto plane_mvp = proj * camera * m_canvas->m_plane_transform[plane_index] * glm::translate(glm::vec3(0, 0, -1));
-                ui::ShaderManager::u_mat4(kShaderUniform::MVP, plane_mvp);
                 if (!(m_canvas->m_erase && m_canvas->m_show_tmp && m_canvas->m_current_layer_idx == layer_index))
                 {
                     ui::ShaderManager::u_float(kShaderUniform::Alpha, m_canvas->m_layers[layer_index].m_opacity);

engine/shader.h

@@ -29,6 +29,7 @@ enum class kShader : uint16_t
     Stroke      = const_hash("stroke"),
     StrokeErase = const_hash("stroke-erase"),
     StrokeLayer = const_hash("stroke-layer"),
+    Checkerboard= const_hash("checkerboard"),
 };
 
 class Shader