From 7b46e71f33913351f0605667cd621cbf77dcb4e1 Mon Sep 17 00:00:00 2001
From: Sascha Willems <webmaster@saschawillems.de>
Date: Sat, 25 Apr 2020 12:01:21 +0200
Subject: [PATCH] Added flag to flip vertex position y coordinates

---
 base/VulkanglTFModel.hpp | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/base/VulkanglTFModel.hpp b/base/VulkanglTFModel.hpp
index cf035e67..242b13dc 100644
--- a/base/VulkanglTFModel.hpp
+++ b/base/VulkanglTFModel.hpp
@@ -541,7 +541,8 @@ namespace vkglTF
 	typedef enum FileLoadingFlags {
 		None = 0,
 		PreTransformVertices = 1,
-		PreMultiplyVertexColors = 2
+		PreMultiplyVertexColors = 2,
+		FlipY = 3
 	};
 
 	/*
@@ -1042,9 +1043,10 @@ namespace vkglTF
 			}
 
 			// Pre-Calculations for requested features
-			if ((fileLoadingFlags & FileLoadingFlags::PreTransformVertices) || (fileLoadingFlags & FileLoadingFlags::PreMultiplyVertexColors)) {
+			if ((fileLoadingFlags & FileLoadingFlags::PreTransformVertices) || (fileLoadingFlags & FileLoadingFlags::PreMultiplyVertexColors) || (fileLoadingFlags & FileLoadingFlags::FlipY)) {
 				const bool preTransform = fileLoadingFlags & FileLoadingFlags::PreTransformVertices;
 				const bool preMultiplyColor = fileLoadingFlags & FileLoadingFlags::PreMultiplyVertexColors;
+				const bool flipY = fileLoadingFlags & FileLoadingFlags::FlipY;
 				for (Node* node : linearNodes) {
 					if (node->mesh) {
 						const glm::mat4 localMatrix = node->getMatrix();
@@ -1055,6 +1057,10 @@ namespace vkglTF
 								if (preTransform) {
 									vertex.pos = glm::vec3(localMatrix * glm::vec4(vertex.pos, 1.0f));
 								}
+								// Flip Y-Axis of vertex positions
+								if (preTransform) {
+									vertex.pos.y *= -1.0f;
+								}
 								// Pre-Multiply vertex colors with material base color
 								if (preMultiplyColor) {
 									vertex.color = primitive->material.baseColorFactor * vertex.color;