Makefile: add Debug build diagnostics

src/frame.c

@@ -6,6 +6,7 @@
 #include <math.h>
 #include <omp.h>
 #include <stdint.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -780,6 +781,7 @@ static int owns_source_boundary(const LensTriangle *triangle,
 typedef struct {
   const LensVertex *vertex[3];
   const LensTriangle *triangle;
+  size_t triangle_index;
   double *hdr;
   int width, height;
   double exposure, magnification;
@@ -820,10 +822,24 @@ static int splat_catalog_tile(const Star *stars, size_t count,
                          weights[1] * context->vertex[1]->log_frequency_ratio +
                          weights[2] * context->vertex[2]->log_frequency_ratio;
     const LinearRgb color = blackbody_to_linear_rgb(star->temperature_K * exp(log_g));
-    context->direct_fallbacks += splat_moffat_cached(
+    const double flux = context->exposure * star->amplitude * context->magnification;
+    const int direct_fallback = splat_moffat_cached(
         context->hdr, context->width, context->height, image_x, image_y, color,
-        context->exposure * star->amplitude * context->magnification,
+        flux,
         context->psf, context->psf_cache);
+    context->direct_fallbacks += direct_fallback;
+#ifdef GR_DEBUG
+    if (direct_fallback)
+      /* This is deliberately emitted by the active splat worker: a direct
+       * fallback can be the long-running work a Debug render is waiting on.
+       * Do not add a critical section here; interleaved Debug lines are more
+       * useful than stalling the other workers. */
+      fprintf(stderr,
+              "Debug: %.3f s splat worker %d triangle %zu star %zu uses direct "
+              "PSF fallback (image %.3f, %.3f; flux %.6g).\n",
+              omp_get_wtime(), omp_get_thread_num(), context->triangle_index,
+              s, image_x, image_y, flux);
+#endif
     ++context->images;
   }
   return 0;
@@ -853,7 +869,8 @@ static size_t splat_catalog_triangles(const FrameLensMesh *mesh,
         {vertex[1]->n_infinity[0], vertex[1]->n_infinity[1], vertex[1]->n_infinity[2]},
         {vertex[2]->n_infinity[0], vertex[2]->n_infinity[1], vertex[2]->n_infinity[2]}};
     TriangleSplatContext context = {.vertex = {vertex[0], vertex[1], vertex[2]},
-                                    .triangle = &mesh->triangles[t], .hdr = hdr,
+                                    .triangle = &mesh->triangles[t],
+                                    .triangle_index = t, .hdr = hdr,
                                     .width = width, .height = height,
                                     .exposure = exposure, .magnification = magnification,
                                     .psf = psf, .psf_cache = psf_cache};