add belt mode for support painting

src/kiri/app/paint.js

@@ -17,6 +17,11 @@
  * support regions. For multi-material coloring or other uses, set
  * options.onlyDownwardFacing = false to paint all surfaces.
  *
+ * BELT PRINTER MODE:
+ * For belt printers, surfaces need support when facing "down the belt slope" rather
+ * than straight down. Set options.beltMode = true and provide options.beltAngle (in radians)
+ * to paint surfaces that face down the angled belt direction.
+ *
  * PAINT POINT DATA STRUCTURE:
  * ---------------------------
  * Paint points must be an array of objects with this structure:
@@ -79,6 +84,9 @@ import { THREE } from '../../ext/three.js';
  * @param {THREE.Color} [paintColor] - Color for painted regions (default: light blue)
  * @param {Object} [options] - Optional configuration
  * @param {boolean} [options.onlyDownwardFacing=true] - Only paint on downward-facing surfaces (z-normal < 0)
+ * @param {boolean} [options.beltMode=false] - Enable belt printer mode (paints surfaces facing down belt slope)
+ * @param {number} [options.beltAngle=0] - Belt angle in radians (only used if beltMode is true)
+ * @param {number} [options.supportAngle=45] - Support angle in degrees (cone around down direction)
  * @returns {THREE.Material} The modified material
  */
 function addPaintOverlaySimple(material, paintPoints, paintColor = new THREE.Color(0x4488ff), options = {}) {
@@ -89,6 +97,10 @@ function addPaintOverlaySimple(material, paintPoints, paintColor = new THREE.Col
 
     // Default: only paint downward-facing surfaces (for support painting)
     const onlyDownwardFacing = options.onlyDownwardFacing !== undefined ? options.onlyDownwardFacing : true;
+    const beltMode = options.beltMode || false;
+    const beltAngle = options.beltAngle || 0;
+    const supportAngle = options.supportAngle || 45;
+    const supportThreshold = Math.cos((90 - supportAngle) * Math.PI / 180);
 
     // Store initial paint points reference
     material.userData.paintPoints = paintPoints;
@@ -119,6 +131,9 @@ function addPaintOverlaySimple(material, paintPoints, paintColor = new THREE.Col
         shader.uniforms.paintCount = { value: validPoints.length };
         shader.uniforms.paintColor = { value: paintColor };
         shader.uniforms.onlyDownwardFacing = { value: onlyDownwardFacing };
+        shader.uniforms.beltMode = { value: beltMode };
+        shader.uniforms.beltAngle = { value: beltAngle };
+        shader.uniforms.supportThreshold = { value: supportThreshold };
 
         // Pass model position from vertex shader to fragment shader
         // Paint points are in widget/model space, so we compare against transformed (model space)
@@ -143,6 +158,9 @@ function addPaintOverlaySimple(material, paintPoints, paintColor = new THREE.Col
             uniform int paintCount;
             uniform vec3 paintColor;
             uniform bool onlyDownwardFacing;
+            uniform bool beltMode;
+            uniform float beltAngle;
+            uniform float supportThreshold;
         ` + shader.fragmentShader;
 
         shader.fragmentShader = shader.fragmentShader.replace(
@@ -156,7 +174,20 @@ function addPaintOverlaySimple(material, paintPoints, paintColor = new THREE.Col
             vec3 worldNormal = normalize(cross(posDx, posDy));
 
             // Only paint downward-facing surfaces if option is enabled
-            bool shouldPaint = !onlyDownwardFacing || worldNormal.z < -0.001;
+            bool shouldPaint;
+            if (beltMode) {
+                // Belt mode: mesh is rotated, check if normal points toward world down
+                // World down (0,0,-1) appears as (0, -sin(θ), -cos(θ)) in rotated mesh space
+                // Dot product: normal · (0, -sin(θ), -cos(θ)) = -sin(θ)*ny - cos(θ)*nz
+                float sinAngle = sin(beltAngle);
+                float cosAngle = cos(beltAngle);
+                float rotatedZ = worldNormal.y * sinAngle + worldNormal.z * cosAngle;
+                // Check if within support angle cone from down direction (rotatedZ < -threshold)
+                shouldPaint = !onlyDownwardFacing || rotatedZ < -supportThreshold;
+            } else {
+                // Normal mode: check if normal points downward within support angle cone
+                shouldPaint = !onlyDownwardFacing || worldNormal.z < -supportThreshold;
+            }
             if (shouldPaint) {
                 // Check if this fragment is within any paint sphere
                 bool painted = false;
@@ -206,6 +237,9 @@ function addPaintOverlaySimple(material, paintPoints, paintColor = new THREE.Col
  * @param {THREE.Color} [paintColor] - Color for painted regions (default: light blue)
  * @param {Object} [options] - Optional configuration
  * @param {boolean} [options.onlyDownwardFacing=true] - Only paint on downward-facing surfaces (z-normal < 0)
+ * @param {boolean} [options.beltMode=false] - Enable belt printer mode (paints surfaces facing down belt slope)
+ * @param {number} [options.beltAngle=0] - Belt angle in radians (only used if beltMode is true)
+ * @param {number} [options.supportAngle=45] - Support angle in degrees (cone around down direction)
  * @returns {THREE.Material} The modified material
  */
 function addPaintOverlayTexture(material, paintPoints, paintColor = new THREE.Color(0x4488ff), options = {}) {
@@ -216,6 +250,10 @@ function addPaintOverlayTexture(material, paintPoints, paintColor = new THREE.Co
 
     // Default: only paint downward-facing surfaces (for support painting)
     const onlyDownwardFacing = options.onlyDownwardFacing !== undefined ? options.onlyDownwardFacing : true;
+    const beltMode = options.beltMode || false;
+    const beltAngle = options.beltAngle || 0;
+    const supportAngle = options.supportAngle || 45;
+    const supportThreshold = Math.cos((90 - supportAngle) * Math.PI / 180);
 
     // Store initial paint points reference
     material.userData.paintPoints = paintPoints;
@@ -264,6 +302,9 @@ function addPaintOverlayTexture(material, paintPoints, paintColor = new THREE.Co
         shader.uniforms.paintTexSize = { value: new THREE.Vector2(texWidth, texHeight) };
         shader.uniforms.paintColor = { value: paintColor };
         shader.uniforms.onlyDownwardFacing = { value: onlyDownwardFacing };
+        shader.uniforms.beltMode = { value: beltMode };
+        shader.uniforms.beltAngle = { value: beltAngle };
+        shader.uniforms.supportThreshold = { value: supportThreshold };
 
         // Pass model position from vertex shader to fragment shader
         // Paint points are in widget/model space, so we compare against transformed (model space)
@@ -289,6 +330,9 @@ function addPaintOverlayTexture(material, paintPoints, paintColor = new THREE.Co
             uniform vec2 paintTexSize;
             uniform vec3 paintColor;
             uniform bool onlyDownwardFacing;
+            uniform bool beltMode;
+            uniform float beltAngle;
+            uniform float supportThreshold;
         ` + shader.fragmentShader;
 
         shader.fragmentShader = shader.fragmentShader.replace(
@@ -302,7 +346,20 @@ function addPaintOverlayTexture(material, paintPoints, paintColor = new THREE.Co
             vec3 worldNormal = normalize(cross(posDx, posDy));
 
             // Only paint downward-facing surfaces if option is enabled
-            bool shouldPaint = !onlyDownwardFacing || worldNormal.z < -0.001;
+            bool shouldPaint;
+            if (beltMode) {
+                // Belt mode: mesh is rotated, check if normal points toward world down
+                // World down (0,0,-1) appears as (0, -sin(θ), -cos(θ)) in rotated mesh space
+                // Dot product: normal · (0, -sin(θ), -cos(θ)) = -sin(θ)*ny - cos(θ)*nz
+                float sinAngle = sin(beltAngle);
+                float cosAngle = cos(beltAngle);
+                float rotatedZ = worldNormal.y * sinAngle + worldNormal.z * cosAngle;
+                // Check if within support angle cone from down direction (rotatedZ < -threshold)
+                shouldPaint = !onlyDownwardFacing || rotatedZ < -supportThreshold;
+            } else {
+                // Normal mode: check if normal points downward within support angle cone
+                shouldPaint = !onlyDownwardFacing || worldNormal.z < -supportThreshold;
+            }
             if (shouldPaint) {
                 bool painted = false;
 

src/kiri/mode/fdm/app/init-ui.js

@@ -267,7 +267,30 @@ function supportStart({ remove } = { remove: false }) {
         return api.widgets.meshes();
     };
     api.feature.on_mouse_drag = ({ int }) => {
-        if (int?.length && int[0].face.normal.z < 0) {
+        // Calculate if surface needs support based on belt mode or normal mode
+        let needsSupport = false;
+        if (int?.length) {
+            const settings = api.conf.get();
+            const normal = int[0].face.normal;
+
+            // Get support angle threshold (how steep before needing support)
+            const supportAngle = settings.process.sliceSupportAngle || 45;
+            const supportThreshold = Math.cos((90 - supportAngle) * Math.PI / 180);
+
+            if (settings.device.bedBelt) {
+                // Belt mode: check if surface will face downward after belt rotation
+                // After rotating by angle θ around X: nz' = ny*sin(θ) + nz*cos(θ)
+                // We want nz' < -threshold (within cone of support angle from down)
+                const angle = (settings.process.sliceAngle || 45) * Math.PI / 180;
+                const rotatedZ = normal.y * Math.sin(angle) + normal.z * Math.cos(angle);
+                needsSupport = rotatedZ < -supportThreshold;
+            } else {
+                // Normal mode: check if normal points downward within support angle cone
+                needsSupport = normal.z < -supportThreshold;
+            }
+        }
+
+        if (needsSupport) {
             supportUpdate(int[0].point, down.widget, remove);
         }
         return [ down.widget.mesh ];
@@ -279,6 +302,12 @@ function supportStart({ remove } = { remove: false }) {
     const scheme = colorSchemeRegistry.getScheme(mode, theme);
     const paintColor = scheme.operations?.paint?.overlay ?? 0x4488ff;
 
+    // Get belt configuration for paint constraint
+    const settings = api.conf.get();
+    const isBelt = settings.device.bedBelt;
+    const beltAngle = isBelt ? (settings.process.sliceAngle || 45) : 0;
+    const supportAngle = settings.process.sliceSupportAngle || 45;
+
     api.widgets.each(w => {
         // Use pushVisualState to track the paint operation
         w.pushVisualState('paint', {
@@ -295,7 +324,11 @@ function supportStart({ remove } = { remove: false }) {
         if (!w.anno.paint) {
             w.anno.paint = [];
         }
-        addPaintOverlayTexture(mat, w.anno.paint, new THREE.Color(paintColor));
+        addPaintOverlayTexture(mat, w.anno.paint, new THREE.Color(paintColor), {
+            beltMode: isBelt,
+            beltAngle: beltAngle * Math.PI / 180,  // Convert to radians
+            supportAngle: settings.process.sliceSupportAngle || 45
+        });
     })
     api.space.update();
 }