diff --git a/art.hpp b/art.hpp
index fd438b7..b39663e 100644
--- a/art.hpp
+++ b/art.hpp
@@ -7,6 +7,7 @@
 
 
 #include "pixelbuffer.h"
+#include "imgui.h"
 #include "imgui_elements.h"
 
 
@@ -27,14 +28,25 @@ class Art {
     bool gui() {
         if (pb)
             ScrollableSliderUInt("Max pixels", &pixel_buffer_maximum, 1, pixel_buffer_maximum_max, "%d", pixel_buffer_maximum/16);
-        return render_gui();
+        bool up = render_gui();
+
+        ImGui::Text("pixels drawn %d, discarded %d",
+            pixels_drawn, pixels_discarded);
+
+        if (pb)
+            ImGui::Text("pixel_buffer_size %d",
+                pb->buffer.size());
+
+        return up;
     }
     void draw(uint32_t *p) {
+        bool direct = render(p);
         if (pb) {
             pb->trunc(pixel_buffer_maximum);
             render_pixel_buffer(p);
+        } else if (!direct) {
+            std::copy(pixels.begin(), pixels.end(), p);
         }
-        render(p);
     }
     virtual void load(std::string json) {};
     virtual std::string save() { return ""; };
@@ -62,10 +74,8 @@ class Art {
 
     virtual ~Art() = default;
 
-    unsigned pixels_drawn = 0;
-    unsigned pixels_discarded = 0;
     unsigned frame_number = 0, clear_every = 0;
-    unsigned pixel_buffer_maximum = 1024*10, pixel_buffer_maximum_max = 1024*64;
+    unsigned pixel_buffer_maximum = 1024*10, pixel_buffer_maximum_max = 1024*1024;
 
     void clear() {
         fill0(pixels);
@@ -75,15 +85,26 @@ class Art {
 private:
     virtual void resize(int _w, int _h) {default_resize(_w, _h);};
     virtual bool render_gui() = 0;
-    virtual void render(uint32_t *p) = 0;
+    virtual bool render(uint32_t *p) = 0;
 
     void render_pixel_buffer(uint32_t *screen) {
+        std::fill_n(screen, w*h, 0);
+#if 1
+        auto b = pb->buffer.begin();
+        auto pbm = pb->buffer.size() > pixel_buffer_maximum ? pixel_buffer_maximum : pb->buffer.size();
+        auto end = pb->buffer.begin() + pbm;
+        for (; b != end; ++b)
+            drawdot(screen, b->x, b->y, b->color);
+#else
         for (auto &p : pb->buffer)
             drawdot(screen, p.x, p.y, p.color);
+#endif
     }
 
 
 protected:
+    unsigned pixels_drawn = 0;
+    unsigned pixels_discarded = 0;
     void default_resize(int _w, int _h) {
         w = _w;
         h = _h;
diff --git a/cloudlife.cpp b/cloudlife.cpp
index 125702b..9915544 100644
--- a/cloudlife.cpp
+++ b/cloudlife.cpp
@@ -23,7 +23,7 @@
  * documentation.  No representations are made about the suitability of this
  * software for any purpose.  It is provided "as is" without express or
  * implied warranty.
- 
+
  * Dear ImGui port by Pavel Vasilyev <yekm@299792458.ru>, Jan 2023
  */
 
@@ -243,7 +243,7 @@ unsigned int Cloudlife::do_tick()
     return count;
 }
 
-void Cloudlife::render(uint32_t *p) {
+bool Cloudlife::render(uint32_t *p) {
     unsigned int count = 0;
 
     for (int i=0; i<f->ticks_per_frame; ++i)
@@ -270,8 +270,7 @@ void Cloudlife::render(uint32_t *p) {
     draw_field();
     cycles++;
 
-    std::copy(pixels.begin(), pixels.end(), p);
-
+    return false;
 }
 
 
diff --git a/cloudlife.hpp b/cloudlife.hpp
index f207ea6..33c9c77 100644
--- a/cloudlife.hpp
+++ b/cloudlife.hpp
@@ -25,7 +25,7 @@ class Cloudlife : public Art {
 private:
     virtual bool render_gui() override;
     virtual void resize(int _w, int _h) override;
-    virtual void render(uint32_t *p) override;
+    virtual bool render(uint32_t *p) override;
     std::unique_ptr<struct field> f;
 
     unsigned ncolors=512;
diff --git a/discrete.cpp b/discrete.cpp
index 227fdea..b7f0e69 100644
--- a/discrete.cpp
+++ b/discrete.cpp
@@ -53,6 +53,7 @@ static enum ftypes bias[BIASES] =
 
 void Discrete::init_discrete()
 {
+	pb.reset();
 	discrete = discretestruct{};
 	double      range;
 	discretestruct *hp = &discrete;
@@ -172,7 +173,8 @@ void Discrete::init_discrete()
 				break;
 			}
 		case THORNBIRD:
-				hp->b = 0.1;
+			pb = std::make_unique<PixelBuffer>();
+			hp->b = 0.1;
 			hp->i = hp->j = 0.1;
 
 			/* select frequencies for parameter variation */
@@ -323,21 +325,22 @@ void Discrete::draw_discrete_1()
 			break;
 		}
 		if (hp->op == THORNBIRD) {
-				x = (short) (hp->maxx / 2 * (1
-								+ sint*hp->j + cost*cosp*hp->i - cost*sinp*hp->b));
-				y = (short) (hp->maxy / 2 * (1
-								- cost*hp->j + sint*cosp*hp->i - sint*sinp*hp->b));
+			x = (short) (hp->maxx / 2 * (1
+							+ sint*hp->j + cost*cosp*hp->i - cost*sinp*hp->b));
+			y = (short) (hp->maxy / 2 * (1
+							- cost*hp->j + sint*cosp*hp->i - sint*sinp*hp->b));
+			pb->append({x, y, pal.get_color(count - k)});
 		}
 		else {
 			x = hp->maxx / 2 + (int) ((hp->i - hp->ic) * hp->is);
 			y = hp->maxy / 2 - (int) ((hp->j - hp->jc) * hp->js);
+			drawdot(x, y, pal.get_color(count - k));
 		}
-		drawdot(x, y, pal.get_color(k));
 	}
 
 }
 
-void Discrete::render(uint32_t *p)
+bool Discrete::render(uint32_t *p)
 {
 	discretestruct *hp = &discrete;
 	int i;
@@ -347,13 +350,14 @@ void Discrete::render(uint32_t *p)
 		hp->count++;
 	}
 
-	std::copy(pixels.begin(), pixels.end(), p);
 	//if (hp->op == THORNBIRD)
 	//	clear();
 
 	if (hp->count > cycles) {
 		resize(w, h);
 	}
+
+	return false;
 }
 
 
diff --git a/ifs.cpp b/ifs.cpp
index a6a046f..d0bdeab 100644
--- a/ifs.cpp
+++ b/ifs.cpp
@@ -241,7 +241,7 @@ IFS::iterate(int count, int p)
 /* Come on and iterate, iterate, iterate and sing... *
  * Yeah, this function just calls iterate, mutate,   *
  * and then draws everything.                        */
-void IFS::render(uint32_t *p)
+bool IFS::render(uint32_t *p)
 {
   int i;
   int partcolor, x, y;
@@ -285,7 +285,7 @@ void IFS::render(uint32_t *p)
     mutate(&lenses[i]);
   }
 
-  std::copy(pixels.begin(), pixels.end(), p);
+  return false;
 }
 
 
diff --git a/ifs.h b/ifs.h
index 9696507..9200421 100644
--- a/ifs.h
+++ b/ifs.h
@@ -22,7 +22,7 @@ class IFS : public Art {
 private:
     virtual bool render_gui() override;
     virtual void resize(int _w, int _h) override;
-    virtual void render(uint32_t *p) override;
+    virtual bool render(uint32_t *p) override;
 
     int ncolours = 1024;
     int ccolour;
diff --git a/main.cpp b/main.cpp
index 90e1648..ded3200 100644
--- a/main.cpp
+++ b/main.cpp
@@ -201,9 +201,6 @@ int main(int argc, char *argv[])
 
         bool reinit = art->gui();
 
-        ImGui::Text("pixels drawn %d, discarded %d",
-            art->pixels_drawn, art->pixels_discarded);
-
         ImGui::Text("Application average %.3f ms/frame (%.1f FPS)",
                     1000.0f / ImGui::GetIO().Framerate,
                     ImGui::GetIO().Framerate);
diff --git a/mtron.cpp b/mtron.cpp
index 86df42b..d93ecd9 100644
--- a/mtron.cpp
+++ b/mtron.cpp
@@ -38,7 +38,7 @@ void Minskytron::dt(uint32_t *p, int x, int y, double o, uint32_t c) {
     p[ y*W + x ] = c | ((unsigned)(0xff*o)<<24);
 }
 
-void Minskytron::render(uint32_t *p) {
+bool Minskytron::render(uint32_t *p) {
     //clear();
     //std::fill(p, p+TEXTURE_SIZE, 0);
     memset(p, 0, TEXTURE_SIZE);
@@ -74,7 +74,7 @@ void Minskytron::render(uint32_t *p) {
         ++i;
     }
 
-    //std::copy(pixels.begin(), pixels.end(), p);
+    return true;
 }
 
 bool Minskytron::render_gui() {
diff --git a/mtron.hpp b/mtron.hpp
index 44e1a01..4bba2a7 100644
--- a/mtron.hpp
+++ b/mtron.hpp
@@ -21,7 +21,7 @@ class Minskytron : public Art {
 private:
     virtual bool render_gui() override;
     //virtual void resize(int _w, int _h) override;
-    virtual void render(uint32_t *p) override;
+    virtual bool render(uint32_t *p) override;
 
     void reinit();
     void dt(uint32_t *p, int x, int y, double o, uint32_t c);
diff --git a/vermiculate.cpp b/vermiculate.cpp
index a0d7dd0..27f1551 100644
--- a/vermiculate.cpp
+++ b/vermiculate.cpp
@@ -641,7 +641,7 @@ bool Vermiculate::move (unsigned char thr)
   return (!LP->dead);
 }
 
-void Vermiculate::render (uint32_t *p)
+bool Vermiculate::render (uint32_t *p)
 {
   int had_instring = (instring != 0);
   int tick = 0;
@@ -695,7 +695,7 @@ void Vermiculate::render (uint32_t *p)
   if (loop++ < cycles)
     goto AGAIN;
 
-  std::copy(pixels.begin(), pixels.end(), p);
+  return false;
 }
 
 bool Vermiculate::render_gui ()
diff --git a/vermiculate.h b/vermiculate.h
index eed6cb0..532b414 100644
--- a/vermiculate.h
+++ b/vermiculate.h
@@ -37,7 +37,7 @@ class Vermiculate : public Art {
 private:
     virtual bool render_gui() override;
     virtual void resize(int _w, int _h) override;
-    virtual void render(uint32_t *p) override;
+    virtual bool render(uint32_t *p) override;
 
   int speed = 1;
   bool erasing, cleared, autopal;