Add samples SecondaryCommandBuffer and SeparateImageSampler. (#331)

+ made some helper functions more explicit.

samples/utils/math.cpp

@@ -29,7 +29,7 @@ namespace vk
 
       glm::mat4x4 model = glm::mat4x4(1.0f);
       glm::mat4x4 view = glm::lookAt(glm::vec3(-5.0f, 3.0f, -10.0f), glm::vec3(0.0f, 0.0f, 0.0f), glm::vec3(0.0f, -1.0f, 0.0f));
-      glm::mat4x4 projection = glm::perspective(fov, static_cast<float>(extent.width) / static_cast<float>(extent.height), 0.1f, 100.0f);
+      glm::mat4x4 projection = glm::perspective(fov, 1.0f, 0.1f, 100.0f);
       glm::mat4x4 clip = glm::mat4x4(1.0f, 0.0f, 0.0f, 0.0f, 0.0f, -1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.5f, 0.0f, 0.0f, 0.0f, 0.5f, 1.0f);   // vulkan clip space has inverted y and half z !
       return clip * projection * view * model;
     }