[cogl/wip/cogl-hair-no-banding: 2/3] cogl-hair: slant shells to avoid banding

[Robert Bragg <rbragg src gnome org>]

commit 7eacd8801f6a2b6a336d45f45ea16b2ea0029914
Author: Robert Bragg <robert linux intel com>
Date:   Mon Mar 5 12:28:45 2012 +0000

    cogl-hair: slant shells to avoid banding
    
    As an experiment this patch adds a varying slant to all of the shells so
    that they are not parallel to avoid them becoming invisible when they
    are parallel with the viewing direction.
    
    This still needs some further work though because the shell textures
    need to be updated according to the sloping too otherwise they don't
    appear to extrude the hair continuously from a single point.

 examples/cogl-hair.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 58 insertions(+), 1 deletion(-)
---
diff --git a/examples/cogl-hair.c b/examples/cogl-hair.c
index 1f731a2..7471cb3 100644
--- a/examples/cogl-hair.c
+++ b/examples/cogl-hair.c
@@ -57,6 +57,7 @@ typedef struct _Data
   int hair_pos_locations[N_TEXTURES];
   int progress_locations[N_TEXTURES];
   int light_dir_locations[N_TEXTURES];
+  int slant_locations[N_TEXTURES];
 
   GTimer *timer;
 
@@ -249,6 +250,9 @@ paint (CoglFramebuffer *fb, Data *data)
   float rotation;
   int i;
   int group_count;
+  float slant[4] = { 1, 0.1, 1, 0.05};
+  float slant_scale = 0.2;
+  int slant_dir = 0;
 
   cogl_framebuffer_clear4f (fb, COGL_BUFFER_BIT_COLOR|COGL_BUFFER_BIT_DEPTH,
                             0, 0, 0, 1);
@@ -272,6 +276,7 @@ paint (CoglFramebuffer *fb, Data *data)
    * scaled and translated.
    */
   cogl_framebuffer_rotate (fb, rotation, 0, 0, 1);
+  //cogl_framebuffer_rotate (fb, 90, 0, 1, 0);
   cogl_framebuffer_rotate (fb, rotation, 0, 1, 0);
   cogl_framebuffer_rotate (fb, rotation, 1, 0, 0);
 
@@ -296,10 +301,54 @@ paint (CoglFramebuffer *fb, Data *data)
                                            4, /* n_components */
                                            1, /* count */
                                            light_dir);
+          cogl_pipeline_set_uniform_float (data->crate_pipelines[i],
+                                           data->slant_locations[i],
+                                           4, /* n_components */
+                                           1, /* count */
+                                           slant);
 
           /* Give Cogl some geometry to draw. */
           cogl_framebuffer_draw_primitive (fb, data->crate_pipelines[i],
                                            data->prim);
+
+#if 0
+          slant[0] =  1 - slant[0];
+          slant[1] = - slant[1];
+          slant[2] =  1 - slant[2];
+          slant[3] = - slant[3];
+#endif
+          slant_dir = (slant_dir + 1) % 4;
+          //slant_dir = 3;
+          switch (slant_dir)
+            {
+            case 0:
+              slant[0] = 1;
+              slant[1] = slant_scale;
+              slant[2] = 0;
+              slant[3] = 0;
+              break;
+            case 1:
+              slant[0] = 0;
+              slant[1] = -slant_scale;
+              slant[2] = 0;
+              slant[3] = 0;
+              break;
+            case 2:
+              slant[0] = 0;
+              slant[1] = 0;
+              slant[2] = 1;
+              slant[3] = slant_scale;
+              break;
+            case 3:
+              slant[0] = 0;
+              slant[1] = 0;
+              slant[2] = 0;
+              slant[3] = -slant_scale;
+              break;
+            default:
+              g_warn_if_reached ();
+            }
+
         }
     }
 
@@ -523,6 +572,7 @@ main (int argc, char **argv)
                               "uniform float hair_pos;\n" /* range [0,length] */
                               "uniform float progress;\n" /* range [0,1] */
                               "uniform vec4 light_dir;\n"
+                              "uniform vec4 slant;\n"
 
                               "float tip_flop = " TIP_FLOP_STR ";\n"
                               "vec4 normal4;\n"
@@ -534,10 +584,15 @@ main (int argc, char **argv)
 
   cogl_snippet_set_replace (snippet,
                             "  normal4 = vec4 (cogl_normal_in, 0.0);\n"
-                            "  cogl_position_out = cogl_position_in + normal4 * hair_pos;\n"
+                            "  cogl_position_out = cogl_position_in + normal4 * "
+                            "    (hair_pos + "
+                            "      ((slant.x - cogl_tex_coord0_in.s) * slant.y) +"
+                            "      ((slant.z - cogl_tex_coord0_in.t) * slant.w));\n"
                             "  cogl_position_out = cogl_modelview_projection_matrix * cogl_position_out;\n"
+#if 1
                             "  force_factor = pow (progress, 3.0) * tip_flop;\n"
                             "  cogl_position_out += hair_force_dir * force_factor;\n"
+#endif
                             "  world_normal = cogl_modelview_matrix * normal4;\n");
 
   cogl_pipeline_add_snippet (template_pipeline, snippet);
@@ -608,6 +663,8 @@ main (int argc, char **argv)
         cogl_pipeline_get_uniform_location (data.crate_pipelines[i], "progress");
       data.light_dir_locations[i] =
         cogl_pipeline_get_uniform_location (data.crate_pipelines[i], "light_dir");
+      data.slant_locations[i] =
+        cogl_pipeline_get_uniform_location (data.crate_pipelines[i], "slant");
     }