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Two-sided lighting, rename misleading draw-count stat

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Two bugs conflated as "weird colors":

1. Two-sided lighting.  IFC placements often embed reflection
   matrices (mirrored families).  Transforming a_normal by
   mat3(inst.transform) produces a normal pointing the wrong way
   on those instances, and max(n·L, 0) then clamps the surface to
   pure ambient — reads as dark / washed out.  Use gl_FrontFacing
   to flip n in the fragment shader so both winding orientations
   shade correctly.  The proper fix (ship an inverse-transpose
   normal matrix or a det-sign bit per instance) is still owed;
   that would unlock re-enabling GL_CULL_FACE for a big fragment-
   work win on closed solids.

2. Stats label "inst_draws" was counting indirect sub-draws, not
   actual GL draw calls — misleading since MDI collapses N sub-
   draws into one glMultiDrawElementsIndirect.  Split into
   gl_draw_calls (real GL calls, = drawn-model count) and
   indirect_sub_draws (packed sub-commands).  For a BIM model
   with 47k unique meshes at full view this now correctly reads
   "1 gl_draws (47092 sub)" rather than suggesting 47k driver
   dispatches.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Dion Moult
2026-04-12 21:10:27 +10:00
parent f0e3056d0a
commit f532624dc1
3 changed files with 22 additions and 9 deletions
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src/ifcviewer/ViewportWindow.cpp
+14 -5
View File
@@ -123,7 +123,13 @@ uniform vec3 u_light_dir;
out vec4 frag_color;
void main() {
// Two-sided lighting: IFC placements frequently embed reflections
// (mirrored families), which flip triangle winding and invert the
// transformed normal. Taking abs(dot) — or equivalently flipping n
// based on gl_FrontFacing — makes both sides shade correctly
// regardless of winding / reflection state.
vec3 n = normalize(v_normal);
if (!gl_FrontFacing) n = -n;
float ndotl = max(dot(n, u_light_dir), 0.0);
float ambient = 0.25;
float diffuse = 0.75 * ndotl;
@@ -906,7 +912,8 @@ void ViewportWindow::render() {
visible_triangles_ = 0;
visible_objects_ = 0;
instanced_draws_ = 0;
gl_draw_calls_ = 0;
indirect_sub_draws_ = 0;
for (auto& [model_id, m] : models_gpu_) {
if (m.hidden || !m.ssbo || m.ssbo_instance_count == 0) continue;
@@ -926,7 +933,8 @@ void ViewportWindow::render() {
visible_triangles_ += (cmd.count / 3) * cmd.instanceCount;
visible_objects_ += cmd.instanceCount;
}
instanced_draws_ += m.indirect_command_count;
indirect_sub_draws_ += m.indirect_command_count;
++gl_draw_calls_;
}
gl_->glBindBuffer(GL_DRAW_INDIRECT_BUFFER, 0);
@@ -964,16 +972,17 @@ void ViewportWindow::render() {
stats.total_triangles = total_tri;
stats.visible_triangles = visible_triangles_;
stats.unique_meshes = total_meshes;
stats.instanced_draws = instanced_draws_;
stats.gl_draw_calls = gl_draw_calls_;
stats.indirect_sub_draws = indirect_sub_draws_;
emit frameStatsUpdated(stats);
qDebug("[frame] %.1f fps %.2f ms obj %u/%u tri %u/%u "
"meshes %u inst_draws %u "
"meshes %u gl_draws %u sub_draws %u "
"vram %.1f MB (vbo %.1f + ebo %.1f + ssbo %.1f) models %zu (%zu hidden)",
last_fps_, 1000.0f / last_fps_,
visible_objects_, total_obj,
visible_triangles_, total_tri,
total_meshes, instanced_draws_,
total_meshes, gl_draw_calls_, indirect_sub_draws_,
(total_vbo + total_ebo + total_ssbo) / (1024.0*1024.0),
total_vbo / (1024.0*1024.0),
total_ebo / (1024.0*1024.0),