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Have border width pre-multiply by alpha, and don't use a separate texture for that border width

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This commit is contained in:
Grant Sanderson 2024-08-20 22:03:45 -05:00
parent d0cb5b4eea
commit dfc5f152dd
3 changed files with 30 additions and 53 deletions
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44
manimlib/shader_wrapper.py
View file

@ -249,13 +249,22 @@ class VShaderWrapper(ShaderWrapper):
geometry_shader=self.program_code["fill_geom"],
fragment_shader=self.program_code["fill_frag"],
)
self.fill_border_program = get_shader_program(
self.ctx,
vertex_shader=self.program_code["stroke_vert"],
geometry_shader=self.program_code["stroke_geom"],
fragment_shader=self.program_code["stroke_frag"].replace(
"// MODIFY FRAG COLOR",
"frag_color.a *= 0.95; frag_color.rgb *= frag_color.a;",
)
)
self.fill_depth_program = get_shader_program(
self.ctx,
vertex_shader=self.program_code["depth_vert"],
geometry_shader=self.program_code["depth_geom"],
fragment_shader=self.program_code["depth_frag"],
)
self.programs = [self.stroke_program, self.fill_program, self.fill_depth_program]
self.programs = [self.stroke_program, self.fill_program, self.fill_border_program, self.fill_depth_program]
# Full vert format looks like this (total of 4x23 = 92 bytes):
# point 3
@ -296,7 +305,7 @@ class VShaderWrapper(ShaderWrapper):
mode=self.render_primitive,
)
self.fill_border_vao = self.ctx.vertex_array(
program=self.stroke_program,
program=self.fill_border_program,
content=[(self.vbo, self.fill_border_vert_format, *self.fill_border_vert_attributes)],
mode=self.render_primitive,
)
@ -325,12 +334,7 @@ class VShaderWrapper(ShaderWrapper):
return
original_fbo = self.ctx.fbo
fill_tx_fbo, fill_tx_vao, border_tx_fbo, border_tx_vao, depth_tx_fbo = self.fill_canvas
# First, draw the border for antialiasing
border_tx_fbo.clear()
border_tx_fbo.use()
self.fill_border_vao.render()
fill_tx_fbo, fill_tx_vao, depth_tx_fbo = self.fill_canvas
# Render to a separate texture, due to strange alpha compositing
# for the blended winding calculation
@ -340,13 +344,13 @@ class VShaderWrapper(ShaderWrapper):
# Be sure not to apply depth test while rendering fill
# but set it back to where it was after
apply_depth_test = bool(gl.glGetBooleanv(gl.GL_DEPTH_TEST))
self.ctx.disable(moderngl.DEPTH_TEST)
# With this blend function, the effect of blending alpha a with
# -a / (1 - a) cancels out, so we can cancel positively and negatively
# oriented triangles
gl.glBlendFuncSeparate(
gl.GL_SRC_ALPHA, gl.GL_ONE_MINUS_SRC_ALPHA,
# With this blend function, the effect of blending alpha a with
# -a / (1 - a) cancels out, so we can cancel positively and negatively
# oriented triangles
gl.GL_ONE_MINUS_DST_ALPHA, gl.GL_ONE
)
self.fill_vao.render()
@ -359,18 +363,20 @@ class VShaderWrapper(ShaderWrapper):
self.fill_depth_vao.render()
self.ctx.enable(moderngl.DEPTH_TEST)
# Render fill onto the border_width fbo
# two alphas, before compositing back to the rest of the scene
border_tx_fbo.use()
gl.glEnable(gl.GL_BLEND)
# Now add border, just taking the max alpha
gl.glBlendFunc(gl.GL_ONE, gl.GL_ONE)
gl.glBlendEquation(gl.GL_MAX)
self.fill_border_vao.render()
# Take the texture we were just drawing to, and render it to
# the main scene. Account for how alphas have been premultiplied
original_fbo.use()
gl.glBlendFunc(gl.GL_ONE, gl.GL_ONE_MINUS_SRC_ALPHA)
gl.glBlendEquation(gl.GL_FUNC_ADD)
fill_tx_vao.render()
original_fbo.use()
# Return to original blending state
gl.glBlendFunc(gl.GL_SRC_ALPHA, gl.GL_ONE_MINUS_SRC_ALPHA)
gl.glBlendEquation(gl.GL_FUNC_ADD)
border_tx_vao.render()
def render(self):
if self.stroke_behind:

2
manimlib/shaders/quadratic_bezier/stroke/frag.glsl
View file

@ -13,4 +13,6 @@ void main() {
// sdf for the region around the curve we wish to color.
float signed_dist_to_region = abs(dist_to_aaw) - half_width_to_aaw;
frag_color.a *= smoothstep(0.5, -0.5, signed_dist_to_region);
// This line is replaced in VShaderWrapper
// MODIFY FRAG COLOR
}

37
manimlib/utils/shaders.py
View file

@ -153,13 +153,10 @@ def get_fill_canvas(ctx: moderngl.Context) -> Tuple[Framebuffer, VertexArray]:
# Important to make sure dtype is floating point (not fixed point)
# so that alpha values can be negative and are not clipped
fill_texture = ctx.texture(size=size, components=4, dtype='f2')
# Use a separate texture to firset render the antialiased border
border_texture = ctx.texture(size=size, components=4, dtype='f1')
# Use yet another one to keep track of depth
# Use another one to keep track of depth
depth_texture = ctx.texture(size=size, components=1, dtype='f4')
fill_texture_fbo = ctx.framebuffer(fill_texture)
border_texture_fbo = ctx.framebuffer(border_texture)
depth_texture_fbo = ctx.framebuffer(depth_texture)
simple_vert = '''
@ -187,38 +184,18 @@ def get_fill_canvas(ctx: moderngl.Context) -> Tuple[Framebuffer, VertexArray]:
if(color.a == 0) discard;
// Counteract scaling in fill frag
color.a *= 1.06;
// Cancel out what was effectively a premultiplication
color.rgb /= color.a;
color *= 1.06;
gl_FragDepth = texture(DepthTexture, uv)[0];
}
'''
simple_frag = '''
#version 330
uniform sampler2D Texture;
in vec2 uv;
out vec4 color;
void main() {
color = texture(Texture, uv);
if(color.a == 0) discard;
}
'''
fill_program = ctx.program(
vertex_shader=simple_vert,
fragment_shader=alpha_adjust_frag,
)
border_program = ctx.program(
vertex_shader=simple_vert,
fragment_shader=simple_frag,
)
fill_program['Texture'].value = get_texture_id(fill_texture)
fill_program['DepthTexture'].value = get_texture_id(depth_texture)
border_program['Texture'].value = get_texture_id(border_texture)
verts = np.array([[0, 0], [0, 1], [1, 0], [1, 1]])
simple_vbo = ctx.buffer(verts.astype('f4').tobytes())
@ -226,12 +203,4 @@ def get_fill_canvas(ctx: moderngl.Context) -> Tuple[Framebuffer, VertexArray]:
fill_program, simple_vbo, 'texcoord',
mode=moderngl.TRIANGLE_STRIP
)
border_texture_vao = ctx.simple_vertex_array(
border_program, simple_vbo, 'texcoord',
mode=moderngl.TRIANGLE_STRIP
)
return (
fill_texture_fbo, fill_texture_vao,
border_texture_fbo, border_texture_vao,
depth_texture_fbo,
)
return (fill_texture_fbo, fill_texture_vao, depth_texture_fbo)