simplified case

libs/math_algos.h

@@ -3398,6 +3398,37 @@ requires is_mat<t_mat>
 }
 
 
+/**
+ * parallel projection matrix (homogeneous 4x4)
+ * set bZ01=false for gl (near and far planes at -1 and +1), and bZ01=true for vk (planes at 0 and 1)
+ * @see https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/glOrtho.xml
+ * @see https://github.com/PacktPublishing/Vulkan-Cookbook/blob/master/Library/Source%20Files/10%20Helper%20Recipes/05%20Preparing%20an%20orthographic%20projection%20matrix.cpp
+ */
+template<class t_mat>
+t_mat hom_parallel_sym(
+	typename t_mat::value_type n = 0.01, typename t_mat::value_type f = 100.,
+	typename t_mat::value_type w = 4, typename t_mat::value_type h = 4.,
+	bool bInvZ = false, bool bZ01 = false, bool bInvY = false)
+requires is_mat<t_mat>
+{
+	using T = typename t_mat::value_type;
+
+	const T d = n - f;
+
+	const T sc = bZ01 ? T(1) : T(2);
+	const T f0 = bZ01 ? T(0) : f;
+	const T ys = bInvY ? T(-1) : T(1);
+	const T zs = bInvZ ? T(-1) : T(1);
+
+	return create<t_mat>({
+		T(2)/w,   0.,         0.,        0.,
+		0,        T(2)*ys/h,  0.,        0.,
+		0.,       0.,         sc*zs/d,   zs*(n+f0)/d,
+		0.,       0.,         0.,        1.
+	});
+}
+
+
 /**
  * viewport matrix (homogeneous 4x4)
  * @see https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/glViewport.xml

qt/vk-4-phys/qttst.cpp

@@ -1206,8 +1206,8 @@ void VkRenderer::UpdatePerspective()
 	// orthogonal projection
 	else
 	{
-		m_matPerspective = m::hom_parallel<t_mat>(
-			0.01, 100., -4., 4., -4, 4., false, true, true);
+		m_matPerspective = m::hom_parallel_sym<t_mat>(
+			0.01, 100., 4., 4., false, true, true);
 	}
 
 	std::tie(m_matPerspective_inv, std::ignore) = m::inv<t_mat, t_vec>(m_matPerspective);