Use Mesh::tti in v2::extract_texture(...)

This means that texture maps with seams will now be extracted correctly. The number of triangles in tvi and tti is identical, and we just need to use tti for the target image where we write to.

Also added asserts that check what is given is valid.

include/eos/render/texture_extraction.hpp

@@ -553,6 +553,13 @@ extract_texture(const core::Mesh& mesh, glm::mat4x4 view_model_matrix, glm::mat4
                 glm::vec4 /*viewport, not needed at the moment */, const eos::core::Image4u& image,
                 bool /* compute_view_angle, unused atm */, int isomap_resolution = 512)
 {
+    // Assert that either there are texture coordinates given for each vertex (in which case the texture map
+    // doesn't contain any seams), or that a separate list of texture triangle indices is given (i.e. mesh.tti
+    // is not empty):
+    assert(mesh.vertices.size() == mesh.texcoords.size() || !mesh.tti.empty());
+    // Sanity check on the texture triangle indices: They should be either empty or equal to tvi.size():
+    assert(mesh.tti.empty() || mesh.tti.size() == mesh.tvi.size());
+
     using detail::divide_by_w;
     using glm::vec2;
     using glm::vec3;
@@ -624,20 +631,30 @@ extract_texture(const core::Mesh& mesh, glm::mat4x4 view_model_matrix, glm::mat4
     const int tex_height =
         isomap_resolution; // keeping this in case we need non-square texture maps at some point
 
-    // Todo: This may need updating to support mesh.tti, potentially like:
-    //   const auto& tti = mesh.tti.empty() ? mesh.tvi : mesh.tti;
-    //   for (const auto& tvi : tti)
-    for (const auto& tvi : mesh.tvi)
+    // Use Mesh::tti as texture triangle indices if present, tvi otherwise:
+    const auto& mesh_tti = mesh.tti.empty() ? mesh.tvi : mesh.tti;
+
+    for (std::size_t triangle_index = 0; triangle_index < mesh.tvi.size(); ++triangle_index)
     {
+        // Select the three indices for the current triangle:
+        const auto& tvi = mesh.tvi[triangle_index];
+        const auto& tti = mesh_tti[triangle_index];
+
+        // Check if all three vertices of the current triangle are visible, and use the triangle if so:
         if (visibility_ray[tvi[0]] && visibility_ray[tvi[1]] &&
             visibility_ray[tvi[2]]) // can also try using ||, but...
         {
-            // Test with a rendered & re-extracted texture shows that we're off by a pixel or more,
-            // definitely need to correct this. Probably here.
-            // It looks like it is 1-2 pixels off. Definitely a bit more than 1.
+            // The model's texcoords become the locations to extract to in the framebuffer (which is the
+            // texture map we're extracting to). The wnd_coords are the coordinates we're extracting from (the
+            // original image), which from the perspective of the rasteriser, is the texture map, and thus
+            // from the rasteriser's perspective they're the texture coords.
+            //
+            // (Note: A test with a rendered & re-extracted texture showed that we're off by a pixel or more,
+            //  definitely need to correct this. Probably here. It looks like it is 1-2 pixels off. Definitely
+            //  a bit more than 1.)
             detail::Vertex<double> pa{
-                vec4(mesh.texcoords[tvi[0]][0] * tex_width,
-					 mesh.texcoords[tvi[0]][1] * tex_height,
+                vec4(mesh.texcoords[tti[0]][0] * tex_width,
+					 mesh.texcoords[tti[0]][1] * tex_height,
                      wnd_coords[tvi[0]].z, // z_ndc
 					 wnd_coords[tvi[0]].w), // 1/w_clip
                 vec3(), // empty
@@ -646,8 +663,8 @@ extract_texture(const core::Mesh& mesh, glm::mat4x4 view_model_matrix, glm::mat4
                     wnd_coords[tvi[0]].y / image.height() // (maybe '1 - wndcoords...'?) wndcoords of the projected/rendered model triangle (in the input img). Normalised to 0,1.
 					)};
             detail::Vertex<double> pb{
-                vec4(mesh.texcoords[tvi[1]][0] * tex_width,
-				mesh.texcoords[tvi[1]][1] * tex_height,
+                vec4(mesh.texcoords[tti[1]][0] * tex_width,
+				mesh.texcoords[tti[1]][1] * tex_height,
                 wnd_coords[tvi[1]].z, // z_ndc
 				wnd_coords[tvi[1]].w), // 1/w_clip
                 vec3(), // empty
@@ -656,8 +673,8 @@ extract_texture(const core::Mesh& mesh, glm::mat4x4 view_model_matrix, glm::mat4
                     wnd_coords[tvi[1]].y / image.height() // (maybe '1 - wndcoords...'?) wndcoords of the projected/rendered model triangle (in the input img). Normalised to 0,1.
 					)};
             detail::Vertex<double> pc{
-                vec4(mesh.texcoords[tvi[2]][0] * tex_width,
-				mesh.texcoords[tvi[2]][1] * tex_height,
+                vec4(mesh.texcoords[tti[2]][0] * tex_width,
+				mesh.texcoords[tti[2]][1] * tex_height,
                 wnd_coords[tvi[2]].z, // z_ndc 
 				wnd_coords[tvi[2]].w), // 1/w_clip
                 vec3(), // empty