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GPU-based Anti-Aliased Line Rendering #233

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2c9ecf3
Implement efficient GPU-based anti-aliased line rendering
nschimme May 22, 2026
a744252
Implement efficient GPU-based anti-aliased line rendering
nschimme May 22, 2026
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8 changes: 5 additions & 3 deletions src/display/Characters.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -107,7 +107,8 @@ void CharacterBatch::CharFakeGL::drawPathSegment(const glm::vec3 &p1,
const glm::vec3 &p2,
const Color color)
{
mmgl::generateLineQuadsSafe(m_pathLineQuads, p1, p2, PATH_LINE_WIDTH, color);
m_pathLines.emplace_back(color, p1);
m_pathLines.emplace_back(color, p2);
}

void CharacterBatch::drawPreSpammedPath(const Coordinate &c1,
Expand Down Expand Up @@ -359,8 +360,9 @@ void CharacterBatch::CharFakeGL::reallyDrawPaths(OpenGL &gl)
= GLRenderState().withDepthFunction(std::nullopt).withBlend(BlendModeEnum::TRANSPARENCY);

gl.renderPoints(m_pathPoints, blended_noDepth.withPointSize(PATH_POINT_SIZE));
if (!m_pathLineQuads.empty()) {
gl.renderColoredQuads(m_pathLineQuads, blended_noDepth);
if (!m_pathLines.empty()) {
gl.renderColoredLines(m_pathLines,
blended_noDepth.withLineParams(LineParams{PATH_LINE_WIDTH}));
}
}

Expand Down
2 changes: 1 addition & 1 deletion src/display/Characters.h
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Original file line number Diff line number Diff line change
Expand Up @@ -105,7 +105,7 @@ class NODISCARD CharacterBatch final
std::vector<ColorVert> m_charLines;
std::vector<ColoredTexVert> m_charRoomQuads;
std::vector<ColorVert> m_pathPoints;
std::vector<ColorVert> m_pathLineQuads;
std::vector<ColorVert> m_pathLines;
std::vector<FontVert3d> m_screenSpaceArrows;
std::vector<GLText> m_names;
std::map<Coordinate, int, CoordCompare> m_coordCounts;
Expand Down
8 changes: 7 additions & 1 deletion src/display/Infomarks.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -144,7 +144,8 @@ void InfomarksBatch::drawLine(const glm::vec3 &a, const glm::vec3 &b)
const glm::vec3 start_v = a + m_offset;
const glm::vec3 end_v = b + m_offset;

mmgl::generateLineQuadsSafe(m_quads, start_v, end_v, INFOMARK_ARROW_LINE_WIDTH, m_color);
m_lines.emplace_back(m_color, start_v);
m_lines.emplace_back(m_color, end_v);
}

void InfomarksBatch::drawTriangle(const glm::vec3 &a, const glm::vec3 &b, const glm::vec3 &c)
Expand Down Expand Up @@ -172,6 +173,7 @@ InfomarksMeshes InfomarksBatch::getMeshes()
auto &gl = m_realGL;
result.points = gl.createPointBatch(m_points);
result.tris = gl.createColoredTriBatch(m_tris);
result.lines = gl.createColoredLineBatch(m_lines);
result.quads = gl.createColoredQuadBatch(m_quads);

{
Expand All @@ -193,6 +195,9 @@ void InfomarksBatch::renderImmediate(const GLRenderState &state)
if (!m_tris.empty()) {
gl.renderColoredTris(m_tris, state);
}
if (!m_lines.empty()) {
gl.renderColoredLines(m_lines, state.withLineParams(LineParams{INFOMARK_ARROW_LINE_WIDTH}));
}
if (!m_quads.empty()) {
gl.renderColoredQuads(m_quads, state);
}
Expand All @@ -215,6 +220,7 @@ void InfomarksMeshes::render()

points.render(common_state.withPointSize(INFOMARK_POINT_SIZE));
tris.render(common_state);
lines.render(common_state.withLineParams(LineParams{INFOMARK_ARROW_LINE_WIDTH}));
quads.render(common_state);
textMesh.render(common_state);
}
Expand Down
2 changes: 2 additions & 0 deletions src/display/Infomarks.h
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@ struct NODISCARD InfomarksMeshes final
{
UniqueMesh points;
UniqueMesh tris;
UniqueMesh lines;
UniqueMesh quads;
UniqueMesh textMesh;
bool isValid = false;
Expand All @@ -41,6 +42,7 @@ struct NODISCARD InfomarksBatch final

std::vector<ColorVert> m_points;
std::vector<ColorVert> m_tris;
std::vector<ColorVert> m_lines;
std::vector<ColorVert> m_quads;

// REVISIT: This is ill-advised and may contain bugs.
Expand Down
20 changes: 20 additions & 0 deletions src/resources/shaders/legacy/line/acolor/frag.glsl
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Original file line number Diff line number Diff line change
@@ -1,10 +1,30 @@
uniform vec4 uColor;

in vec4 vColor;
in vec2 vUv;
in float vLineLength;
in float vWidth;

out vec4 vFragmentColor;

void main()
{
float halfWidth = vWidth * 0.5;

// Calculate distance to the segment
float dx = max(-vUv.x, 0.0) + max(vUv.x - vLineLength, 0.0);
float dy = vUv.y;
float dist = sqrt(dx * dx + dy * dy);

// Anti-aliasing
// Smoothstep creates a nice alpha ramp over 1 pixel
float feather = 1.0;
float alpha = 1.0 - smoothstep(halfWidth - feather, halfWidth + feather, dist);

if (alpha <= 0.0) {
discard;
}

vFragmentColor = vColor * uColor;
vFragmentColor.a *= alpha;
}
39 changes: 34 additions & 5 deletions src/resources/shaders/legacy/line/acolor/vert.glsl
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,9 @@ layout(location = 1) in vec3 aVert1;
layout(location = 2) in vec3 aVert2;

out vec4 vColor;
out vec2 vUv;
out float vLineLength;
out float vWidth;
Comment on lines +11 to +12

@sourcery-ai sourcery-ai Bot May 22, 2026

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suggestion (performance): Consider marking vLineLength and vWidth as flat to avoid unnecessary interpolation and potential precision issues.

These values are per-line, not per-vertex, so they should be declared as flat out float in the vertex shader and flat in float in the fragment shader to reflect their per-primitive nature rather than being interpolated per-fragment.

Suggested implementation:

out vec4 vColor;
out vec2 vUv;
flat out float vLineLength;
flat out float vWidth;

In the matching fragment shader for this pipeline (likely something like src/resources/shaders/legacy/line/acolor/frag.glsl), update the corresponding varyings to:

  • Replace in float vLineLength; with flat in float vLineLength;
  • Replace in float vWidth; with flat in float vWidth;

This will ensure the per-line values are not interpolated per-fragment and avoids GLSL interface mismatch between vertex and fragment shaders.


void main()
{
Expand All @@ -15,9 +18,11 @@ void main()
vec4 clip1 = uMVP * vec4(aVert1, 1.0);
vec4 clip2 = uMVP * vec4(aVert2, 1.0);

// Standard perspective divide
vec2 ndc1 = clip1.xy / clip1.w;
vec2 ndc2 = clip2.xy / clip2.w;

// Screen coordinates
vec2 screen1 = (ndc1 + 1.0) * 0.5 * vec2(uViewport.zw);
vec2 screen2 = (ndc2 + 1.0) * 0.5 * vec2(uViewport.zw);

Expand All @@ -30,14 +35,38 @@ void main()
}
vec2 normal = vec2(-dir.y, dir.x);

vec2 offset = normal * uLineWidth * 0.5;
// Padding for anti-aliasing (e.g. 1 pixel)
float feather = 1.0;
float halfWidth = uLineWidth * 0.5;
float totalHalfWidth = halfWidth + feather;

vLineLength = len;
vWidth = uLineWidth;

vec2 pos;
float z;
if (gl_VertexID == 0) { pos = screen1 + offset; z = clip1.z / clip1.w; }
else if (gl_VertexID == 1) { pos = screen1 - offset; z = clip1.z / clip1.w; }
else if (gl_VertexID == 2) { pos = screen2 - offset; z = clip2.z / clip2.w; }
else { pos = screen2 + offset; z = clip2.z / clip2.w; }

// Expand longitudinally to allow for round caps
vec2 offsetL = dir * totalHalfWidth;
vec2 offsetP = normal * totalHalfWidth;

if (gl_VertexID == 0) {
pos = screen1 - offsetL + offsetP;
z = clip1.z / clip1.w;
vUv = vec2(-totalHalfWidth, totalHalfWidth);
} else if (gl_VertexID == 1) {
pos = screen1 - offsetL - offsetP;
z = clip1.z / clip1.w;
vUv = vec2(-totalHalfWidth, -totalHalfWidth);
} else if (gl_VertexID == 2) {
pos = screen2 + offsetL - offsetP;
z = clip2.z / clip2.w;
vUv = vec2(len + totalHalfWidth, -totalHalfWidth);
} else { // gl_VertexID == 3
pos = screen2 + offsetL + offsetP;
z = clip2.z / clip2.w;
vUv = vec2(len + totalHalfWidth, totalHalfWidth);
}

vec2 final_ndc = (pos / vec2(uViewport.zw)) * 2.0 - 1.0;
gl_Position = vec4(final_ndc, z, 1.0);
Expand Down
18 changes: 18 additions & 0 deletions src/resources/shaders/legacy/line/ucolor/frag.glsl
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Original file line number Diff line number Diff line change
@@ -1,8 +1,26 @@
uniform vec4 uColor;

in vec2 vUv;
in float vLineLength;
in float vWidth;

out vec4 vFragmentColor;

void main()
{
float halfWidth = vWidth * 0.5;

float dx = max(-vUv.x, 0.0) + max(vUv.x - vLineLength, 0.0);
float dy = vUv.y;
float dist = sqrt(dx * dx + dy * dy);

float feather = 1.0;
float alpha = 1.0 - smoothstep(halfWidth - feather, halfWidth + feather, dist);

if (alpha <= 0.0) {
discard;
}

vFragmentColor = uColor;
vFragmentColor.a *= alpha;
}
36 changes: 31 additions & 5 deletions src/resources/shaders/legacy/line/ucolor/vert.glsl
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Expand Up @@ -5,6 +5,10 @@ uniform ivec4 uViewport; // x, y, width, height
layout(location = 0) in vec3 aVert1;
layout(location = 1) in vec3 aVert2;

out vec2 vUv;
out float vLineLength;
out float vWidth;

void main()
{
vec4 clip1 = uMVP * vec4(aVert1, 1.0);
Expand All @@ -25,14 +29,36 @@ void main()
}
vec2 normal = vec2(-dir.y, dir.x);

vec2 offset = normal * uLineWidth * 0.5;
float feather = 1.0;
float halfWidth = uLineWidth * 0.5;
float totalHalfWidth = halfWidth + feather;
Comment on lines +32 to +34

@sourcery-ai sourcery-ai Bot May 22, 2026

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suggestion: The hardcoded feather value is duplicated and could drift from the fragment shader; consider sharing it via a uniform or constant.

feather = 1.0 is set both here and in the fragment shader. If only one is updated later, the geometry expansion and alpha falloff will diverge. Please use a shared uniform or common constant/define so feather stays consistent and AA tuning is centralized.

Suggested implementation:

uniform mat4 uMVP;
uniform float uFeather;


    // Anti-aliasing
    // Smoothstep creates a nice alpha ramp over 1 pixel
    float feather = uFeather;
    float alpha = 1.0 - smoothstep(halfWidth - feather, halfWidth + feather, dist);

To fully centralize and share the feather parameter:

  1. In the corresponding fragment shader (likely src/resources/shaders/legacy/line/ucolor/frag.glsl), declare uniform float uFeather; and replace any float feather = 1.0; with float feather = uFeather;.
  2. In the rendering code that binds this shader, set the uFeather uniform once (e.g., via glUniform1f) so both vertex and fragment shaders receive the same value.
  3. Optionally, define uFeather in a common include GLSL file if your shader system supports shared includes, so future line shaders can reuse the same AA parameter.


vLineLength = len;
vWidth = uLineWidth;

vec2 pos;
float z;
if (gl_VertexID == 0) { pos = screen1 + offset; z = clip1.z / clip1.w; }
else if (gl_VertexID == 1) { pos = screen1 - offset; z = clip1.z / clip1.w; }
else if (gl_VertexID == 2) { pos = screen2 - offset; z = clip2.z / clip2.w; }
else { pos = screen2 + offset; z = clip2.z / clip2.w; }

vec2 offsetL = dir * totalHalfWidth;
vec2 offsetP = normal * totalHalfWidth;

if (gl_VertexID == 0) {
pos = screen1 - offsetL + offsetP;
z = clip1.z / clip1.w;
vUv = vec2(-totalHalfWidth, totalHalfWidth);
} else if (gl_VertexID == 1) {
pos = screen1 - offsetL - offsetP;
z = clip1.z / clip1.w;
vUv = vec2(-totalHalfWidth, -totalHalfWidth);
} else if (gl_VertexID == 2) {
pos = screen2 + offsetL - offsetP;
z = clip2.z / clip2.w;
vUv = vec2(len + totalHalfWidth, -totalHalfWidth);
} else {
pos = screen2 + offsetL + offsetP;
z = clip2.z / clip2.w;
vUv = vec2(len + totalHalfWidth, totalHalfWidth);
}

vec2 final_ndc = (pos / vec2(uViewport.zw)) * 2.0 - 1.0;
gl_Position = vec4(final_ndc, z, 1.0);
Expand Down
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