[#26] Verify content of loaded Mesh struct.

This commit adds code to the first_mesh project that actually tests the
content of the Mesh struct returned by loadMesh() rather than just
checking the returned integer.

projects/first_mesh/src/main.cpp

 #include <iostream>
+#include <stdio.h>
 #include <vkcv/asset/asset_loader.hpp>
 
+
 int main(int argc, const char** argv) {
 	vkcv::asset::Mesh mesh;
 	
-	int result = vkcv::asset::loadMesh("resources/cube/cube.gltf", mesh);
+	const char *path = argc > 1 ? argv[1] : "resources/cube/cube.gltf";
+	int result = vkcv::asset::loadMesh(path, mesh);
 	
 	if (result == 1) {
 		std::cout << "Mesh loading successful!" << std::endl;
 	} else {
 		std::cout << "Mesh loading failed: " << result << std::endl;
+		return 1;
+	}
+
+	/* Demonstration of how to use the vkcv::asset::Mesh struct. */
+	const char *primitive_modes[] = {
+		"points", "lines", "line loop", "line strip", "triangles",
+		"triangle strip", "triangle fan"
+	};
+	printf("Mesh %s (%s) has %lu vertex group(s) and %lu material(s):\n",
+			mesh.name.c_str(), path, mesh.vertexGroups.size(),
+			mesh.materials.size());
+	for (size_t i = 0; i < mesh.vertexGroups.size(); i++) {
+		printf("--- vertex group %lu ---\n", i);
+		const auto &vg = mesh.vertexGroups[i];
+		printf("primitive mode: %d (%s)\n", vg.mode,
+				primitive_modes[vg.mode]);
+		printf("index buffer: %lu bytes for %lu indices (offset into "
+				"%p is %u)\n", vg.indexBuffer.byteLength,
+				vg.numIndices, vg.indexBuffer.data,
+				vg.indexBuffer.byteOffset);
+		uint16_t *indices = (uint16_t*)vg.indexBuffer.data;
+		printf("\tindices: ");
+		for (size_t j = 0; j < vg.numIndices; j++) {
+			printf("%u ", indices[j]);
+		}
+		printf("\n");
+		printf("vertex buffer: %lu bytes for %lu vertices with %lu "
+				"attributes (starting at %p)\n",
+				vg.vertexBuffer.byteLength, vg.numVertices,
+				vg.vertexBuffer.attributes.size(),
+				vg.vertexBuffer.data);
 	}
 	
 	return 0;