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Have corners emitted by stroke geom shader better line up with bezier control points

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This is helpful for, say, setting variable stroke width
This commit is contained in:
Grant Sanderson
2023-01-11 21:30:12 -08:00
parent 1f04ba92fb
commit 131e1c2eeb
1 changed files with 22 additions and 27 deletions
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49
manimlib/shaders/quadratic_bezier_stroke/geom.glsl
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@ -1,7 +1,7 @@
#version 330
layout (triangles) in;
layout (triangle_strip, max_vertices = 5) out;
layout (triangle_strip, max_vertices = 6) out;
// Needed for get_gl_Position
uniform vec2 frame_shape;
@ -79,14 +79,16 @@ void create_joint(float angle, vec2 unit_tan, float buff,
// This function is responsible for finding the corners of
// a bounding region around the bezier curve, which can be
// emitted as a triangle fan
int get_corners(
// emitted as a triangle fan, with vertices vaguely close
// to control points so that the passage of vert data to
// frag shaders is most natural.
void get_corners(
vec2 controls[3],
float stroke_widths[3],
float aaw, // Anti-alias width
float angle_from_prev,
float angle_to_next,
out vec2 corners[5]
out vec2 corners[6]
){
vec2 p0 = controls[0];
vec2 p1 = controls[1];
@ -104,25 +106,20 @@ int get_corners(
float buff0 = 0.5 * stroke_widths[0] + aaw;
float buff2 = 0.5 * stroke_widths[2] + aaw;
// The order of corners should be for a triangle_strip.
vec2 c0 = p0 - buff0 * p0_perp;
vec2 c1 = p0 + buff0 * p0_perp;
vec2 c2 = p2 + buff2 * p2_perp;
vec2 c3 = p2 - buff2 * p2_perp;
vec2 c2 = p1 - 0.5 * (buff0 * p0_perp + buff2 * p2_perp);
// c3 needs to be defined after c5
vec2 c4 = p2 - buff2 * p2_perp;
vec2 c5 = p2 + buff2 * p2_perp;
vec2 c3 = 0.5 * (c1 + c5);
// Account for previous and next control points
create_joint(angle_from_prev, v01, buff0, c0, c0, c1, c1);
create_joint(angle_to_next, -v12, buff2, c3, c3, c2, c2);
create_joint(angle_to_next, -v12, buff2, c4, c4, c5, c5);
// Linear case is the simplest
if(bool(is_linear)){
// The order of corners should be for a triangle_strip. Last entry is a dummy
corners = vec2[5](c0, c1, c3, c2, vec2(0.0));
return 4;
}
// Otherwise, form a pentagon around the curve
corners = vec2[5](c0, c1, p1, c2, c3);
corners[2] -= buff0 * p0_perp + buff2 * p2_perp;
return 5;
corners = vec2[6](c0, c1, c2, c3, c4, c5);
}
@ -177,24 +174,22 @@ void main() {
uv_anti_alias_width = uv_scale_factor * scaled_aaw;
// Corners of a bounding region around curve
vec2 corners[5];
int n_corners = get_corners(
vec2 corners[6];
get_corners(
flat_verts, scaled_strokes, scaled_aaw,
angle_from_prev, angle_to_next,
corners
);
int index_map[5] = int[5](0, 0, 1, 2, 2);
if(n_corners == 4) index_map[2] = 2;
// Emit each corner
for(int i = 0; i < n_corners; i++){
for(int i = 0; i < 6; i++){
int vert_index = i / 2;
uv_coords = (xy_to_uv * vec3(corners[i], 1.0)).xy;
uv_stroke_width = uv_scale_factor * scaled_strokes[index_map[i]];
uv_stroke_width = uv_scale_factor * scaled_strokes[vert_index];
// Apply some lighting to the color before sending out.
vec3 xyz_coords = vec3(corners[i], verts[index_map[i]].z);
vec3 xyz_coords = vec3(corners[i], verts[vert_index].z);
color = finalize_color(
v_color[index_map[i]],
v_color[vert_index],
xyz_coords,
unit_normal,
light_source_position,
@ -203,7 +198,7 @@ void main() {
gloss,
shadow
);
gl_Position = get_gl_Position(vec3(corners[i], verts[index_map[i]].z));
gl_Position = get_gl_Position(vec3(corners[i], verts[vert_index].z));
EmitVertex();
}
EndPrimitive();