Fix tessellation artifacts

.github/workflows/screenshot.yml

@@ -0,0 +1,36 @@
+name: Screenshot Test
+
+on:
+  push:
+    branches: [ "fix/tessellation-artifacts" ]
+
+jobs:
+  test-and-screenshot:
+    runs-on: ubuntu-22.04
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Install dependencies
+      run: sudo apt update && sudo apt install --fix-missing cmake gcc gfortran libx11-dev libglu1-mesa-dev libmotif-dev tcsh libxaw7-dev libglew-dev libdlm-dev libgl2ps-dev libpng-dev xvfb imagemagick
+
+    - name: Build
+      run: |
+        make config
+        make build
+
+    - name: Run test_f3 and capture screenshot
+      run: |
+        Xvfb :99 -screen 0 1024x768x24 &
+        export DISPLAY=:99
+        sleep 2
+        ./build/test_f/test_f3 &
+        TEST_PID=$!
+        sleep 5
+        import -window root test_f3_output.png
+        kill $TEST_PID
+
+    - name: Upload Screenshot Artifact
+      uses: actions/upload-artifact@v4
+      with:
+        name: test_f3-screenshot
+        path: test_f3_output.png

src/libphigs/f_binding/fb_extel.c

@@ -884,3 +884,38 @@ FTN_SUBROUTINE(psmcv3)(
   spacelist.half_spaces = &list[0];
   pset_model_clip_vol3(iop, spacelist);
 }
+
+/*******************************************************************************
+ * psbici
+ *
+ * DESCR:   set back interior colour index
+ * RETURNS:   N/A
+ */
+FTN_SUBROUTINE(psbici)(
+                      FTN_INTEGER(coli)
+                      )
+{
+  Pint colr_ind = FTN_INTEGER_GET(coli);
+#ifdef DEBUG
+  printf("DEBUG: pset back interior color index set to %d\n", colr_ind);
+#endif
+  pset_back_int_colr_ind(colr_ind);
+}
+
+/*******************************************************************************
+ * psbisi
+ *
+ * DESCR:   set back interior style index
+ * RETURNS:   N/A
+ */
+FTN_SUBROUTINE(psbisi)(
+                      FTN_INTEGER(stylei)
+                      )
+{
+  Pint style_ind = FTN_INTEGER_GET(stylei);
+#ifdef DEBUG
+  printf("DEBUG: pset back interior style index set to %d\n", style_ind);
+#endif
+  pset_back_int_style_ind(style_ind);
+}
+

src/libphigs/wsgl/wsgl_tess.c

@@ -26,6 +26,10 @@ static void CALLBACK tessEndCB() {
     glEnd();
 }
 
+static void CALLBACK tessEdgeFlagCB(GLboolean flag) {
+    glEdgeFlag(flag);
+}
+
 static void CALLBACK tessVertexCB(void *data) {
     Wsgl_tess_vertex *v = (Wsgl_tess_vertex *)data;
     if (v->has_norm) {
@@ -83,6 +87,9 @@ void wsgl_draw_tess_polygon(Wsgl_tess_vertex *vertices, int num_vertices, int re
     int normal_indices[MAX_VERTICES];
     int n_vertices = 0;
     int n_normals = 0;
+    GLboolean orig_depth_mask;
+    GLfloat cur_color[4];
+    int has_transparency = 0;
 
     tess = gluNewTess();
     if (!tess) return;
@@ -92,6 +99,25 @@ void wsgl_draw_tess_polygon(Wsgl_tess_vertex *vertices, int num_vertices, int re
     gluTessCallback(tess, GLU_TESS_VERTEX, (void (CALLBACK *)())tessVertexCB);
     gluTessCallback(tess, GLU_TESS_ERROR, (void (CALLBACK *)())tessErrorCB);
     gluTessCallback(tess, GLU_TESS_COMBINE, (void (CALLBACK *)())tessCombineCB);
+    gluTessCallback(tess, GLU_TESS_EDGE_FLAG, (void (CALLBACK *)())tessEdgeFlagCB);
+
+    /* Determine if depth writing should be disabled for order-independent transparency */
+    glGetBooleanv(GL_DEPTH_WRITEMASK, &orig_depth_mask);
+
+    if (num_vertices > 0 && vertices[0].apply_cb) {
+        if (vertices[0].colr_type == PMODEL_RGBA && vertices[0].colr.direct.rgba.alpha < 1.0f) {
+            has_transparency = 1;
+        }
+    } else {
+        glGetFloatv(GL_CURRENT_COLOR, cur_color);
+        if (cur_color[3] < 1.0f) {
+            has_transparency = 1;
+        }
+    }
+
+    if (has_transparency && orig_depth_mask == GL_TRUE) {
+        glDepthMask(GL_FALSE);
+    }
 
     gluTessBeginPolygon(tess, NULL);
     gluTessBeginContour(tess);
@@ -115,6 +141,13 @@ void wsgl_draw_tess_polygon(Wsgl_tess_vertex *vertices, int num_vertices, int re
     gluTessEndPolygon(tess);
     gluDeleteTess(tess);
 
+    /* Restore default edge flag state for subsequent rendering */
+    glEdgeFlag(GL_TRUE);
+
+    if (has_transparency && orig_depth_mask == GL_TRUE) {
+        glDepthMask(GL_TRUE);
+    }
+
     if (record_geom_flag && n_vertices > 0) {
         wsgl_add_geometry(GEOM_FACE, vertex_indices, normal_indices, n_vertices);
     }