fix truncated join cutoff + some cleanup

GLMakie/assets/shader/lines.frag

@@ -8,9 +8,7 @@ struct Nothing{ //Nothing type, to encode if some variable doesn't contain any d
 
 in vec4 f_color;
 in vec4 f_quad_sdf;
-in vec2 f_joint_cutoff;
-// in float f_line_width;
-// in float f_cumulative_length;
+in vec4 f_joint_cutoff;
 in vec2 f_uv;
 flat in vec4 f_pattern_overwrite;
 flat in uvec2 f_id;
@@ -92,6 +90,10 @@ void main(){
     // sdf = max(sdf, abs(f_quad_sdf.z) - f_line_width);
     sdf = max(sdf, max(f_quad_sdf.z, f_quad_sdf.w));
 
+    // smoothly cut off corners of truncated miter joints
+    sdf = max(sdf, max(f_joint_cutoff.z, f_joint_cutoff.w));
+
+    // add pattern
     sdf = max(sdf, get_pattern_sdf(pattern));
 
     // draw

GLMakie/assets/shader/lines.geom

@@ -19,9 +19,7 @@ in float g_thickness[];
 
 out vec4 f_color;
 out vec4 f_quad_sdf; // smooth edges (along length and width)
-out vec2 f_joint_cutoff; // hard edges (joint)
-// out float f_line_width;
-// out float f_cumulative_length;
+out vec4 f_joint_cutoff; // xy = hard cutoff, zw = smooth cutoff
 out vec2 f_uv;
 flat out vec4 f_pattern_overwrite;
 flat out uvec2 f_id;
@@ -58,7 +56,7 @@ How it works:
 struct LineData {
     vec3 p1, p2, v;
     float segment_length, extrusion_a, extrusion_b;
-    vec2 n, miter_v_a, miter_n_a, miter_v_b, miter_n_b;
+    vec2 n, n0, n2, miter_v_a, miter_n_a, miter_v_b, miter_n_b;
     float miter_offset_a, miter_offset_b;
     bool is_start, is_end;
 };
@@ -105,73 +103,37 @@ void process_pattern(sampler1D pattern, LineData line) {
 }
 
 void emit_vertex(vec3 origin, vec2 center, LineData line, int index, vec2 geom_offset) {
+
     vec3 position = origin + geom_offset.x * line.v + vec3(geom_offset.y * line.n, 0);
 
-    // sdf prototyping
+    // sdf generation
+
+    bool is_a_truncated_joint = line.miter_offset_a < 0.5;
+    bool is_b_truncated_joint = line.miter_offset_b < 0.5;
 
-    // joint hard cutoff
-    // TODO Problem: this can cut the whole line even if the next segment does
-    //               fill that space (due to being short for example)
-    // Options:
-    // - don't do this for truncated join -> overlap, need to clean extra corner generated by extrusion
-    // if line start/end move hard cutoff out so smooth rect cutoff can act
     vec2 VP1 = position.xy - line.p1.xy;
     vec2 VP2 = position.xy - line.p2.xy;
-    f_joint_cutoff = vec2(
-        line.is_start ? -10.0 : dot(VP1, -line.miter_v_a),
-        line.is_end   ? -10.0 : dot(VP2,  line.miter_v_b)
-    );
-    // note miter_v_a and miter_v_b are different, so no -width .. + width merge
-    // also no max
-
-
-    // rect
-    // vec2 VC = position.xy - center;
-    // can't have absolute, will break interpolation
-    // f_rect_sdf = vec2(
-    //     abs(dot(VC, v)) - 0.5 * segment_length, // - extrusion, apply in frag? do we need 0 edge?
-    //     abs(dot(VC, n)) - thickness
-    // );
-    // f_rect_sdf = vec2(dot(VC, line.v.xy), dot(VC, line.n));
-
-    // joint soft cutoff
-    // need miter_offset to be big if no truncation
-    // f_joint_smooth = vec2(100.0, 100.0);
-    // if (line.miter_offset_a < 0.5) // truncated join condition
-    //     f_joint_smooth.x = dot(VP1, line.miter_n_a) - 0.5 * g_thickness[1] * line.miter_offset_a;
-    // if (line.miter_offset_b < 0.5) // truncated join condition
-    //     f_joint_smooth.y = dot(VP2, line.miter_n_b) - 0.5 * g_thickness[2] * line.miter_offset_b;
-
-
-    /*
-        #######
-        width sdf:
-            vert/geom: x = dot(vertex_pos - center, line.n)
-            frag:      sd = abs(x) - unpadded_linewidth
-        length sdf:
-            start sdf:
-                vert/geom: x = dot(vertex_pos - P1, -line.v)
-                frag:      sd = x
-            stop sdf:
-                vert/goem: x = dot(vertex_pos - P2, line.v);
-                frag:      sd = x
-            smooth truncated join sdf:
-                vert/geom: x = dot(vertex_pos - P1/P2, sign(dot(miter_v, v)) * miter_v) - miter_distance
-                frag:      sd = x
-            sharp join sdf:
-                vert/geom: x = -10.0
-                frag:      sd = x
-    */
-
-    // SDF in (v dir at P1, v dir at P2, n dir) (default is sharp joint)
-    // f_quad_sdf = vec3(-1.0, -1.0, dot(position.xy - center, line.n));
-    float temp = dot(position.xy - center, line.n);
-    // f_quad_sdf = vec4(-1.0, -1.0, temp - 0.5 * g_thickness[index], 0.5 * g_thickness[index] - temp);
-    f_quad_sdf = vec4(-1.0, -1.0, temp - 0.5 * g_thickness[index], -temp - 0.5 * g_thickness[index]);
 
-    bool is_a_truncated_joint = line.miter_offset_a < 0.5;
-    bool is_b_truncated_joint = line.miter_offset_b < 0.5;
+    // by default joint cutoffs do nothing
+    f_joint_cutoff = vec4(-10.0);
+
+    // sharp joints use sharp (pixelated) cut offs to avoid self-overlap
+    if (!line.is_start && !is_a_truncated_joint)
+        f_joint_cutoff.x = dot(VP1, -line.miter_v_a);
+    if (!line.is_end && !is_b_truncated_joint)
+        f_joint_cutoff.y = dot(VP2, line.miter_v_b);
+
+    // truncated joints use smooth cutoff for corners that are outside the other segment
+    // TODO: this slightly degrades AA quality due to two AA edges overlapping
+    if (is_a_truncated_joint)
+        f_joint_cutoff.z = dot(VP1, -sign(dot(line.v.xy, line.n0)) * line.n0) - 0.5 * g_thickness[1];
+    if (is_b_truncated_joint)
+        f_joint_cutoff.w = dot(VP2,  sign(dot(line.v.xy, line.n2)) * line.n2) - 0.5 * g_thickness[2];
 
+
+    // SDF of quad
+
+    // In line direction
     if (line.is_start) // flat line end
         f_quad_sdf.x = dot(VP1, -line.v.xy);
     else if (is_a_truncated_joint)
@@ -182,14 +144,17 @@ void emit_vertex(vec3 origin, vec2 center, LineData line, int index, vec2 geom_o
     else if (is_b_truncated_joint)
         f_quad_sdf.y = dot(VP2, line.miter_n_b) - 0.5 * g_thickness[2] * line.miter_offset_b;
 
-    // if truncated or no join -> use lw at p
-    // else                    -> use lw at p + dot(miter_n, v) * sign(miter_n, offset dir)
-    // float line_length = line.segment_length;
 
+    // In line normal direction (linewidth)
     // This mostly works
     // TODO: integrate better
     // TODO Problem: you can get concave shapes with very different linewidths + zooming
     // we want to adjust v direction on respective side to dodge both edge normals...
+
+    // start/end/truncated joint: use g_thickness[i] at point i
+    // sharp joint: use g_thickness[i] at point i +- joint offset to avoid different
+    //              linewidth between this and the previous/next segment
+    // TODO: can we calculate this more efficiently?
     // top
     float offset_a = !is_a_truncated_joint && !line.is_start ? line.extrusion_a : 0.0;
     float offset_b = !is_b_truncated_joint && !line.is_end   ? line.extrusion_b : 0.0;
@@ -207,10 +172,11 @@ void emit_vertex(vec3 origin, vec2 center, LineData line, int index, vec2 geom_o
     edge_normal = vec2(-edge_vector.y, edge_vector.x);
     f_quad_sdf.w = dot(position.xy - corner1, -edge_normal);
 
+    // And the simpler things...
     f_color     = g_color[index];
     gl_Position = vec4((2.0 * position.xy / resolution) - 1.0, position.z, 1.0);
     f_id        = g_id[index];
-    // TODO: pattern sampling
+    // index into pattern
     f_uv = vec2(
         (g_lastlen[index] + geom_offset.x) / pattern_length,
         0.5 + geom_offset.y / g_thickness[index]
@@ -304,6 +270,8 @@ void main(void)
     line.p2 = p2;
     line.v = v1;
     line.n = n1;
+    line.n0 = n0;
+    line.n2 = n2;
     line.segment_length = segment_length;
     line.is_start = !isvalid[0];
     line.is_end = !isvalid[3];

GLMakie/src/drawing_primitives.jl

@@ -459,7 +459,7 @@ function draw_atomic(screen::Screen, scene::Scene, @nospecialize(plot::Lines))
             linewidth = gl_attributes[:thickness]
             px_per_unit = data[:px_per_unit]
             data[:pattern] = map(linestyle, linewidth, px_per_unit) do ls, lw, ppu
-                ppu * _mean(lw) .* ls
+                return ppu * _mean(lw) .* ls
             end
             data[:fast] = false