diff --git a/crates/modules/pineal/heatmap/src/encoder.rs b/crates/modules/pineal/heatmap/src/encoder.rs
new file mode 100644
index 0000000..67bcc44
--- /dev/null
+++ b/crates/modules/pineal/heatmap/src/encoder.rs
@@ -0,0 +1,57 @@
+//! Encoder: `HeatmapMatrix` → buffer ARGB para subir como textura.
+
+use crate::matrix::HeatmapMatrix;
+use crate::palette::Ramp;
+
+/// Normaliza cada celda a `[0,1]` por min/max, la mapea por la rampa y
+/// empaqueta el resultado como `u32` ARGB (0xAARRGGBB), fila por fila.
+///
+/// El backend GPUI sube este buffer como una textura y la rendea con un
+/// solo `drawImageRect`, en vez de N draw calls.
+pub fn encode_argb(matrix: &HeatmapMatrix, ramp: Ramp) -> Vec<u32> {
+    let (min, max) = matrix.min_max();
+    let span = max - min;
+    let mut out = Vec::with_capacity(matrix.width() * matrix.height());
+    for &v in matrix.data() {
+        let t = if span > 0.0 { (v - min) / span } else { 0.0 };
+        let c = ramp.sample(t);
+        out.push(pack_argb(c.a, c.r, c.g, c.b));
+    }
+    out
+}
+
+/// Empaqueta 4 canales `f32` `[0,1]` en `0xAARRGGBB`.
+fn pack_argb(a: f32, r: f32, g: f32, b: f32) -> u32 {
+    let q = |v: f32| (v.clamp(0.0, 1.0) * 255.0).round() as u32;
+    (q(a) << 24) | (q(r) << 16) | (q(g) << 8) | q(b)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn encodes_one_pixel_per_cell() {
+        let m = HeatmapMatrix::from_data(vec![0.0, 1.0, 2.0, 3.0], 2, 2).unwrap();
+        let buf = encode_argb(&m, Ramp::Grayscale);
+        assert_eq!(buf.len(), 4);
+    }
+
+    #[test]
+    fn normalizes_min_to_ramp_start() {
+        // Grayscale: min → negro (0x000000), max → blanco (0xffffff).
+        let m = HeatmapMatrix::from_data(vec![10.0, 20.0], 2, 1).unwrap();
+        let buf = encode_argb(&m, Ramp::Grayscale);
+        assert_eq!(buf[0] & 0x00ff_ffff, 0x0000_0000); // min
+        assert_eq!(buf[1] & 0x00ff_ffff, 0x00ff_ffff); // max
+        assert_eq!(buf[0] >> 24, 0xff); // alpha opaco
+    }
+
+    #[test]
+    fn flat_matrix_does_not_divide_by_zero() {
+        let m = HeatmapMatrix::from_data(vec![5.0; 4], 2, 2).unwrap();
+        let buf = encode_argb(&m, Ramp::Viridis);
+        assert_eq!(buf.len(), 4);
+        assert!(buf.iter().all(|&p| p == buf[0]));
+    }
+}
diff --git a/crates/modules/pineal/heatmap/src/lib.rs b/crates/modules/pineal/heatmap/src/lib.rs
index f8575fd..4179864 100644
--- a/crates/modules/pineal/heatmap/src/lib.rs
+++ b/crates/modules/pineal/heatmap/src/lib.rs
@@ -1,21 +1,23 @@
-//! `pineal-heatmap` — matriz `[width × height]` de `f32` → imagen.
+//! `pineal-heatmap` — matriz `width × height` de `f32` → visualización.
 //!
-//! Para matrices grandes (4096² = 67 MB de pixels), encodear la
-//! imagen una vez al cambiar la data y renderear con un solo
-//! `drawImageRect` (o equivalente GPUI). Eso convierte el coste
-//! de cada frame en "blit de una textura", sub-millisecond.
+//! Dos caminos de render:
+//! - [`paint`] — agnóstico, un `fill_rect` por celda contra un `Canvas`.
+//!   Apto para matrices chicas y export SVG.
+//! - [`encoder::encode_argb`] — empaqueta la matriz como buffer ARGB para
+//!   que un backend lo suba como textura y la rendee con un solo blit.
+//!   Apto para matrices grandes (4096² sin sudar).
 //!
-//! - **`matrix`** — `HeatmapMatrix { data: Vec<f32>, width, height,
-//!   revision }`.
-//! - **`palette`** — color ramps (viridis, plasma, gray…).
-//! - **`encoder`** — convierte la matrix a un buffer ARGB para
-//!   subir como textura.
-//! - **`element`** — `Element` GPUI.
+//! - [`matrix`] — `HeatmapMatrix` con `revision` para invalidación.
+//! - [`palette`] — color ramps (Viridis, Grayscale).
 
 #![forbid(unsafe_code)]
-#![allow(dead_code)]
 
-pub mod matrix {}
-pub mod palette {}
-pub mod encoder {}
-pub mod element {}
+pub mod matrix;
+pub mod palette;
+pub mod encoder;
+pub mod paint;
+
+pub use encoder::encode_argb;
+pub use matrix::HeatmapMatrix;
+pub use paint::paint;
+pub use palette::Ramp;
diff --git a/crates/modules/pineal/heatmap/src/matrix.rs b/crates/modules/pineal/heatmap/src/matrix.rs
new file mode 100644
index 0000000..acaeba0
--- /dev/null
+++ b/crates/modules/pineal/heatmap/src/matrix.rs
@@ -0,0 +1,93 @@
+//! `HeatmapMatrix` — matriz densa `width × height` de `f32`.
+
+/// Matriz de valores para un heatmap. `revision` se incrementa en cada
+/// mutación — los backends lo usan para invalidar la textura cacheada.
+#[derive(Debug, Clone)]
+pub struct HeatmapMatrix {
+    data: Vec<f32>,
+    width: usize,
+    height: usize,
+    revision: u64,
+}
+
+impl HeatmapMatrix {
+    /// Matriz de ceros de `width × height`.
+    pub fn new(width: usize, height: usize) -> Self {
+        Self { data: vec![0.0; width * height], width, height, revision: 0 }
+    }
+
+    /// Construye desde datos crudos. `None` si `data.len() != width*height`.
+    pub fn from_data(data: Vec<f32>, width: usize, height: usize) -> Option<Self> {
+        if data.len() != width * height {
+            return None;
+        }
+        Some(Self { data, width, height, revision: 0 })
+    }
+
+    pub fn width(&self) -> usize { self.width }
+    pub fn height(&self) -> usize { self.height }
+    pub fn revision(&self) -> u64 { self.revision }
+    pub fn data(&self) -> &[f32] { &self.data }
+
+    /// Valor en `(x, y)`. `0.0` si está fuera de rango.
+    pub fn get(&self, x: usize, y: usize) -> f32 {
+        if x >= self.width || y >= self.height {
+            return 0.0;
+        }
+        self.data[y * self.width + x]
+    }
+
+    /// Fija el valor en `(x, y)` e incrementa `revision`. No-op si está
+    /// fuera de rango.
+    pub fn set(&mut self, x: usize, y: usize, v: f32) {
+        if x >= self.width || y >= self.height {
+            return;
+        }
+        self.data[y * self.width + x] = v;
+        self.revision += 1;
+    }
+
+    /// Reemplaza todos los datos (mismas dimensiones) e incrementa
+    /// `revision`. No-op si la longitud no coincide.
+    pub fn replace_data(&mut self, data: Vec<f32>) {
+        if data.len() == self.width * self.height {
+            self.data = data;
+            self.revision += 1;
+        }
+    }
+
+    /// `(min, max)` de los valores. `(0.0, 0.0)` si la matriz está vacía.
+    pub fn min_max(&self) -> (f32, f32) {
+        let mut it = self.data.iter().copied();
+        let Some(first) = it.next() else { return (0.0, 0.0) };
+        it.fold((first, first), |(lo, hi), v| (lo.min(v), hi.max(v)))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn from_data_checks_length() {
+        assert!(HeatmapMatrix::from_data(vec![1.0; 6], 2, 3).is_some());
+        assert!(HeatmapMatrix::from_data(vec![1.0; 5], 2, 3).is_none());
+    }
+
+    #[test]
+    fn get_set_and_revision() {
+        let mut m = HeatmapMatrix::new(3, 2);
+        assert_eq!(m.revision(), 0);
+        m.set(1, 1, 4.5);
+        assert_eq!(m.get(1, 1), 4.5);
+        assert_eq!(m.revision(), 1);
+        m.set(99, 99, 1.0); // fuera de rango → no-op
+        assert_eq!(m.revision(), 1);
+    }
+
+    #[test]
+    fn min_max_over_values() {
+        let m = HeatmapMatrix::from_data(vec![3.0, -1.0, 7.0, 2.0], 2, 2).unwrap();
+        assert_eq!(m.min_max(), (-1.0, 7.0));
+    }
+}
diff --git a/crates/modules/pineal/heatmap/src/paint.rs b/crates/modules/pineal/heatmap/src/paint.rs
new file mode 100644
index 0000000..4d0f909
--- /dev/null
+++ b/crates/modules/pineal/heatmap/src/paint.rs
@@ -0,0 +1,61 @@
+//! Painter agnóstico: dibuja una `HeatmapMatrix` contra un `Canvas`.
+//!
+//! Emite un `fill_rect` por celda. Apto para matrices chicas y para
+//! export SVG. Para matrices grandes el backend GPUI usa
+//! [`crate::encoder`] + textura en vez de este camino.
+
+use crate::matrix::HeatmapMatrix;
+use crate::palette::Ramp;
+use pineal_render::{Canvas, Rect};
+
+/// Dibuja `matrix` dentro de `area`, una celda = un `fill_rect`.
+/// Los valores se normalizan por min/max de la matriz.
+pub fn paint(matrix: &HeatmapMatrix, ramp: Ramp, area: Rect, canvas: &mut dyn Canvas) {
+    let (w, h) = (matrix.width(), matrix.height());
+    if w == 0 || h == 0 {
+        return;
+    }
+    let (min, max) = matrix.min_max();
+    let span = max - min;
+    let cell_w = area.w / w as f32;
+    let cell_h = area.h / h as f32;
+
+    for y in 0..h {
+        for x in 0..w {
+            let v = matrix.get(x, y);
+            let t = if span > 0.0 { (v - min) / span } else { 0.0 };
+            let color = ramp.sample(t);
+            let rect = Rect::new(
+                area.x + x as f32 * cell_w,
+                area.y + y as f32 * cell_h,
+                cell_w,
+                cell_h,
+            );
+            canvas.fill_rect(rect, color);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pineal_render::{PlanRecorder, RenderCmd};
+
+    #[test]
+    fn emits_one_fill_rect_per_cell() {
+        let m = HeatmapMatrix::from_data(vec![0.0, 1.0, 2.0, 3.0, 4.0, 5.0], 3, 2).unwrap();
+        let mut rec = PlanRecorder::new();
+        paint(&m, Ramp::Viridis, Rect::new(0.0, 0.0, 300.0, 200.0), &mut rec);
+        let plan = rec.into_plan();
+        assert_eq!(plan.cmds.len(), 6);
+        assert!(plan.cmds.iter().all(|c| matches!(c, RenderCmd::FillRect { .. })));
+    }
+
+    #[test]
+    fn empty_matrix_emits_nothing() {
+        let m = HeatmapMatrix::new(0, 0);
+        let mut rec = PlanRecorder::new();
+        paint(&m, Ramp::Viridis, Rect::new(0.0, 0.0, 10.0, 10.0), &mut rec);
+        assert!(rec.into_plan().cmds.is_empty());
+    }
+}
diff --git a/crates/modules/pineal/heatmap/src/palette.rs b/crates/modules/pineal/heatmap/src/palette.rs
new file mode 100644
index 0000000..14b3ef1
--- /dev/null
+++ b/crates/modules/pineal/heatmap/src/palette.rs
@@ -0,0 +1,94 @@
+//! Color ramps para heatmaps. Interpolación lineal entre control points.
+
+use pineal_render::Color;
+
+/// Rampa de color. `sample(t)` mapea `t ∈ [0,1]` a un `Color`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Ramp {
+    /// Viridis — perceptualmente uniforme, dark-purple → yellow.
+    Viridis,
+    /// Escala de grises lineal, negro → blanco.
+    Grayscale,
+}
+
+impl Ramp {
+    /// Mapea `t` (se clampa a `[0,1]`) a un color de la rampa.
+    pub fn sample(&self, t: f32) -> Color {
+        let t = t.clamp(0.0, 1.0);
+        match self {
+            Ramp::Grayscale => Color::rgb(t, t, t),
+            Ramp::Viridis => lerp_stops(t, VIRIDIS),
+        }
+    }
+}
+
+/// Control points de Viridis (aproximación de 5 stops del colormap real).
+const VIRIDIS: &[(f32, u32)] = &[
+    (0.00, 0x440154),
+    (0.25, 0x3b528b),
+    (0.50, 0x21918c),
+    (0.75, 0x5ec962),
+    (1.00, 0xfde725),
+];
+
+/// Interpola linealmente entre los stops `(pos, hex)` ordenados por `pos`.
+fn lerp_stops(t: f32, stops: &[(f32, u32)]) -> Color {
+    if stops.is_empty() {
+        return Color::BLACK;
+    }
+    if t <= stops[0].0 {
+        return Color::from_hex(stops[0].1);
+    }
+    let last = stops[stops.len() - 1];
+    if t >= last.0 {
+        return Color::from_hex(last.1);
+    }
+    for w in stops.windows(2) {
+        let (p0, c0) = w[0];
+        let (p1, c1) = w[1];
+        if t >= p0 && t <= p1 {
+            let local = (t - p0) / (p1 - p0);
+            return lerp_color(Color::from_hex(c0), Color::from_hex(c1), local);
+        }
+    }
+    Color::from_hex(last.1)
+}
+
+fn lerp_color(a: Color, b: Color, t: f32) -> Color {
+    Color::rgba(
+        a.r + (b.r - a.r) * t,
+        a.g + (b.g - a.g) * t,
+        a.b + (b.b - a.b) * t,
+        a.a + (b.a - a.a) * t,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn grayscale_endpoints() {
+        assert_eq!(Ramp::Grayscale.sample(0.0), Color::BLACK);
+        assert_eq!(Ramp::Grayscale.sample(1.0), Color::WHITE);
+    }
+
+    #[test]
+    fn viridis_endpoints_match_control_points() {
+        assert_eq!(Ramp::Viridis.sample(0.0), Color::from_hex(0x440154));
+        assert_eq!(Ramp::Viridis.sample(1.0), Color::from_hex(0xfde725));
+    }
+
+    #[test]
+    fn sample_clamps_out_of_range() {
+        assert_eq!(Ramp::Viridis.sample(-5.0), Ramp::Viridis.sample(0.0));
+        assert_eq!(Ramp::Viridis.sample(5.0), Ramp::Viridis.sample(1.0));
+    }
+
+    #[test]
+    fn viridis_midpoint_is_between() {
+        let mid = Ramp::Viridis.sample(0.5);
+        // El stop de 0.5 es 0x21918c.
+        assert_eq!(mid, Color::from_hex(0x21918c));
+    }
+}