diff --git a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlay.js b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlay.js
index a728416faf..ad1f2b2189 100644
--- a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlay.js
+++ b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlay.js
@@ -10,9 +10,13 @@ class DeveloperOverlay
 		this.devCommandsOverlay.onPress = this.toggle.bind(this);
 
 		this.checkBoxes = this.getCheckboxNames().map((name, i) =>
-			new DeveloperOverlayCheckbox(
-				new DeveloperOverlayCheckboxes.prototype[name](playerViewControl, selection),
+			new DeveloperOverlayControlCheckbox(
+				new DeveloperOverlayControlCheckboxes.prototype[name](playerViewControl, selection),
 				i));
+		this.dropDowns = this.getDropDownNames().map((name, i) =>
+			new DeveloperOverlayControlDropDown(
+				new DeveloperOverlayControlDrowDowns.prototype[name](playerViewControl, selection),
+				i + this.checkBoxes.length));
 
 		this.resize();
 	}
@@ -22,7 +26,12 @@ class DeveloperOverlay
 	 */
 	getCheckboxNames()
 	{
-		return Object.keys(DeveloperOverlayCheckboxes.prototype);
+		return Object.keys(DeveloperOverlayControlCheckboxes.prototype);
+	}
+
+	getDropDownNames()
+	{
+		return Object.keys(DeveloperOverlayControlDrowDowns.prototype);
 	}
 
 	toggle()
@@ -35,6 +44,9 @@ class DeveloperOverlay
 		this.checkBoxes.forEach(checkbox => {
 			checkbox.setHidden(this.devCommandsOverlay.hidden);
 		});
+		this.dropDowns.forEach(dropDown => {
+			dropDown.setHidden(this.devCommandsOverlay.hidden);
+		});
 	}
 
 	sendNotification()
@@ -59,7 +71,8 @@ class DeveloperOverlay
 		let size = this.devCommandsOverlay.size;
 		size.bottom =
 			size.top +
-			this.checkBoxes.reduce((height, checkbox) => height + checkbox.getHeight(), 0);
+			this.checkBoxes.reduce((height, checkbox) => height + checkbox.getHeight(), 0) +
+			this.dropDowns.reduce((height, dropDown) => height + dropDown.getHeight(), 0);
 		this.devCommandsOverlay.size = size;
 	}
 }
diff --git a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlay.xml b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlay.xml
index 61172c047c..9e3185f37b 100644
--- a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlay.xml
+++ b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlay.xml
@@ -4,15 +4,16 @@
 	name="devCommandsOverlay"
 	type="image"
 	sprite="sessionOverlayBackground"
-	size="100%-250 50%-200 100%-8 50%"
+	size="100%-250 50%-280 100%-8 50%"
 	z="40"
 	hidden="true"
 	hotkey="session.devcommands.toggle"
 >
 	<repeat count="20">
-		<object name="dev_command[n]" size="0 0 100% 20" hidden="true">
-			<object name="dev_command_label[n]" size="0 0 100%-26 100%" type="text" style="devCommandsText"/>
-			<object name="dev_command_checkbox[n]" size="100%-24 1 100% 100%" type="checkbox" style="ModernTickBox"/>
+		<object name="dev_command[n]" size="0 0 100% 24" hidden="true">
+			<object name="dev_command_label[n]" size="0 0 100%-26 100%" type="text" style="devCommandsText" hidden="true"/>
+			<object name="dev_command_checkbox[n]" size="100%-24 1 100% 100%" type="checkbox" style="ModernTickBox" hidden="true"/>
+			<object name="dev_command_dropdown[n]" size="0 0 100% 100%" type="dropdown" style="devCommandsDropDown"  tooltip_style="tooltipInstant" hidden="true"/>
 		</object>
 	</repeat>
 </object>
diff --git a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControl.js b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControl.js
new file mode 100644
index 0000000000..3341b22645
--- /dev/null
+++ b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControl.js
@@ -0,0 +1,35 @@
+/**
+ * Base class for all controls on the developer overlay.
+ */
+class DeveloperOverlayControl
+{
+	constructor(handler, i)
+	{
+		this.handler = handler;
+		this.handler.update = () => this.update();
+
+		this.body = Engine.GetGUIObjectByName("dev_command[" + i + "]");
+		this.resize(i);
+
+		this.updater = this.update.bind(this);
+
+		if (this.handler.checked)
+			registerPlayersInitHandler(this.updater);
+	}
+
+	getHeight()
+	{
+		return this.body.size.bottom - this.body.size.top;
+	}
+
+	resize(i)
+	{
+		let size = this.body.size;
+		let height = size.bottom;
+		size.top = height * i;
+		size.bottom = height * (i + 1);
+		this.body.size = size;
+		this.body.hidden = false;
+	}
+}
+
diff --git a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayCheckbox.js b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlCheckbox.js
similarity index 59%
rename from binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayCheckbox.js
rename to binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlCheckbox.js
index 19b2513760..bf38a81a08 100644
--- a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayCheckbox.js
+++ b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlCheckbox.js
@@ -1,26 +1,19 @@
 /**
  * This class sets up a checkbox in the developer overlay and assigns its specific handler.
  */
-class DeveloperOverlayCheckbox
+class DeveloperOverlayControlCheckbox extends DeveloperOverlayControl
 {
 	constructor(handler, i)
 	{
-		this.handler = handler;
-		this.handler.update = () => this.update();
+		super(handler, i);
 
 		this.label = Engine.GetGUIObjectByName("dev_command_label[" + i + "]");
 		this.label.caption = this.handler.label();
+		this.label.hidden = false;
 
 		this.checkbox = Engine.GetGUIObjectByName("dev_command_checkbox[" + i + "]");
 		this.checkbox.onPress = this.onPress.bind(this);
-
-		this.body = Engine.GetGUIObjectByName("dev_command[" + i + "]");
-		this.resize(i);
-
-		this.updater = this.update.bind(this);
-
-		if (this.handler.checked)
-			registerPlayersInitHandler(this.updater);
+		this.checkbox.hidden = false;
 	}
 
 	onPress()
@@ -47,19 +40,5 @@ class DeveloperOverlayCheckbox
 		else
 			registerSimulationUpdateHandler(this.updater);
 	}
-
-	getHeight()
-	{
-		return this.body.size.bottom - this.body.size.top;
-	}
-
-	resize(i)
-	{
-		let size = this.body.size;
-		let height = size.bottom;
-		size.top = height * i;
-		size.bottom = height * (i + 1);
-		this.body.size = size;
-		this.body.hidden = false;
-	}
 }
+
diff --git a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayCheckboxes.js b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlCheckboxes.js
similarity index 77%
rename from binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayCheckboxes.js
rename to binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlCheckboxes.js
index 0a3a81c7a0..6f5f63cd5a 100644
--- a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayCheckboxes.js
+++ b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlCheckboxes.js
@@ -4,11 +4,11 @@
  * If the class has a checked property, then that will be called every simulation update to
  * synchronize the state of the checkbox (only if the developer overaly is opened).
  */
-class DeveloperOverlayCheckboxes
+class DeveloperOverlayControlCheckboxes
 {
 }
 
-DeveloperOverlayCheckboxes.prototype.ControlAll = class
+DeveloperOverlayControlCheckboxes.prototype.ControlAll = class
 {
 	label()
 	{
@@ -30,7 +30,7 @@ DeveloperOverlayCheckboxes.prototype.ControlAll = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.ChangePerspective = class
+DeveloperOverlayControlCheckboxes.prototype.ChangePerspective = class
 {
 	constructor(playerViewControl)
 	{
@@ -48,7 +48,7 @@ DeveloperOverlayCheckboxes.prototype.ChangePerspective = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.SelectionEntityState = class
+DeveloperOverlayControlCheckboxes.prototype.SelectionEntityState = class
 {
 	constructor(playerViewControl, selection)
 	{
@@ -66,7 +66,7 @@ DeveloperOverlayCheckboxes.prototype.SelectionEntityState = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.PathfinderOverlay = class
+DeveloperOverlayControlCheckboxes.prototype.PathfinderOverlay = class
 {
 	label()
 	{
@@ -79,7 +79,7 @@ DeveloperOverlayCheckboxes.prototype.PathfinderOverlay = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.HierarchicalPathfinderOverlay = class
+DeveloperOverlayControlCheckboxes.prototype.HierarchicalPathfinderOverlay = class
 {
 	label()
 	{
@@ -92,7 +92,7 @@ DeveloperOverlayCheckboxes.prototype.HierarchicalPathfinderOverlay = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.ObstructionOverlay = class
+DeveloperOverlayControlCheckboxes.prototype.ObstructionOverlay = class
 {
 	label()
 	{
@@ -105,7 +105,7 @@ DeveloperOverlayCheckboxes.prototype.ObstructionOverlay = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.UnitMotionOverlay = class
+DeveloperOverlayControlCheckboxes.prototype.UnitMotionOverlay = class
 {
 	label()
 	{
@@ -118,7 +118,7 @@ DeveloperOverlayCheckboxes.prototype.UnitMotionOverlay = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.RangeOverlay = class
+DeveloperOverlayControlCheckboxes.prototype.RangeOverlay = class
 {
 	label()
 	{
@@ -131,7 +131,7 @@ DeveloperOverlayCheckboxes.prototype.RangeOverlay = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.BoundingBoxOverlay = class
+DeveloperOverlayControlCheckboxes.prototype.BoundingBoxOverlay = class
 {
 	label()
 	{
@@ -144,7 +144,7 @@ DeveloperOverlayCheckboxes.prototype.BoundingBoxOverlay = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.RestrictCamera = class
+DeveloperOverlayControlCheckboxes.prototype.RestrictCamera = class
 {
 	label()
 	{
@@ -162,7 +162,7 @@ DeveloperOverlayCheckboxes.prototype.RestrictCamera = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.RevealMap = class
+DeveloperOverlayControlCheckboxes.prototype.RevealMap = class
 {
 	label()
 	{
@@ -183,7 +183,7 @@ DeveloperOverlayCheckboxes.prototype.RevealMap = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.EnableTimeWarp = class
+DeveloperOverlayControlCheckboxes.prototype.EnableTimeWarp = class
 {
 	constructor()
 	{
@@ -202,7 +202,7 @@ DeveloperOverlayCheckboxes.prototype.EnableTimeWarp = class
 };
 
 
-DeveloperOverlayCheckboxes.prototype.ActivateRejoinTest = class
+DeveloperOverlayControlCheckboxes.prototype.ActivateRejoinTest = class
 {
 	constructor()
 	{
@@ -241,7 +241,7 @@ DeveloperOverlayCheckboxes.prototype.ActivateRejoinTest = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.PromoteSelectedUnits = class
+DeveloperOverlayControlCheckboxes.prototype.PromoteSelectedUnits = class
 {
 	label()
 	{
@@ -262,7 +262,7 @@ DeveloperOverlayCheckboxes.prototype.PromoteSelectedUnits = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.EnableCulling = class
+DeveloperOverlayControlCheckboxes.prototype.EnableCulling = class
 {
 	label()
 	{
@@ -280,7 +280,7 @@ DeveloperOverlayCheckboxes.prototype.EnableCulling = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.LockCullCamera = class
+DeveloperOverlayControlCheckboxes.prototype.LockCullCamera = class
 {
 	label()
 	{
@@ -298,7 +298,7 @@ DeveloperOverlayCheckboxes.prototype.LockCullCamera = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.DisplayCameraFrustum = class
+DeveloperOverlayControlCheckboxes.prototype.DisplayCameraFrustum = class
 {
 	label()
 	{
@@ -316,7 +316,7 @@ DeveloperOverlayCheckboxes.prototype.DisplayCameraFrustum = class
 	}
 };
 
-DeveloperOverlayCheckboxes.prototype.DisplayShadowsFrustum = class
+DeveloperOverlayControlCheckboxes.prototype.DisplayShadowsFrustum = class
 {
 	label()
 	{
diff --git a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlDropDown.js b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlDropDown.js
new file mode 100644
index 0000000000..c3b011a154
--- /dev/null
+++ b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlDropDown.js
@@ -0,0 +1,38 @@
+/**
+ * This class sets up a dropdown in the developer overlay and assigns its specific handler.
+ */
+class DeveloperOverlayControlDropDown extends DeveloperOverlayControl
+{
+	constructor(handler, i)
+	{
+		super(handler, i);
+
+		this.dropdown = Engine.GetGUIObjectByName("dev_command_dropdown[" + i + "]");
+		this.dropdown.onSelectionChange = this.onSelectionChange.bind(this);
+		this.dropdown.hidden = false;
+	}
+
+	onSelectionChange()
+	{
+		this.handler.onSelectionChange(this.dropdown.selected);
+		this.update();
+	}
+
+	update()
+	{
+		this.dropdown.list = this.handler.values().map(e => e.label);
+		this.dropdown.list_data = this.handler.values().map(e => e.value);
+		if (this.handler.selected && this.dropdown.selected != this.handler.selected())
+			this.dropdown.selected = this.handler.selected();
+		if (this.handler.enabled)
+			this.dropdown.enabled = this.handler.enabled();
+	}
+
+	setHidden(hidden)
+	{
+		if (hidden)
+			unregisterSimulationUpdateHandler(this.updater);
+		else
+			registerSimulationUpdateHandler(this.updater);
+	}
+}
diff --git a/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlDropDowns.js b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlDropDowns.js
new file mode 100644
index 0000000000..a9230e0624
--- /dev/null
+++ b/binaries/data/mods/public/gui/session/developer_overlay/DeveloperOverlayControlDropDowns.js
@@ -0,0 +1,37 @@
+/**
+ * This class stores the handlers for the individual dropdowns available in the developer overlay.
+ * Such a class must have onSelectionChange function.
+ * If the class has a selected property, then that will be called every simulation update to
+ * synchronize the state of the dropdown (only if the developer overaly is opened).
+ */
+class DeveloperOverlayControlDrowDowns
+{
+}
+
+DeveloperOverlayControlDrowDowns.prototype.RenderDebugMode = class
+{
+	constructor()
+	{
+		this.selectedIndex = this.values().map(e => e.value).indexOf(
+			Engine.Renderer_GetRenderDebugMode());
+	}
+
+	values()
+	{
+		return [
+			{ "value": "RENDER_DEBUG_MODE_NONE", "label": translate("Render Debug Mode Disabled") },
+			{ "value": "RENDER_DEBUG_MODE_AO", "label": translate("Render Debug Mode AO") }
+		];
+	}
+
+	onSelectionChange(selectedIndex)
+	{
+		this.selectedIndex = selectedIndex;
+		Engine.Renderer_SetRenderDebugMode(this.values()[this.selectedIndex].value);
+	}
+
+	selected()
+	{
+		return this.selectedIndex;
+	}
+};
diff --git a/binaries/data/mods/public/gui/session/styles.xml b/binaries/data/mods/public/gui/session/styles.xml
index 0a8c313a42..e3077a97bc 100644
--- a/binaries/data/mods/public/gui/session/styles.xml
+++ b/binaries/data/mods/public/gui/session/styles.xml
@@ -103,11 +103,39 @@
 	/>
 
 	<style name="devCommandsText"
-		font="sans-10"
+		font="sans-12"
 		textcolor="255 255 255"
 		text_align="right"
 	/>
 
+	<style name="devCommandsDropDown"
+		dropdown_buffer="0"
+		font="sans-12"
+		textcolor="white"
+		text_align="left"
+		text_valign="top"
+		button_width="20"
+		sprite_disabled="ModernDarkBoxDisabled"
+		sprite_overlay_disabled="ModernDarkBoxGoldBorderDisabled"
+		sprite2="ModernDropDownArrow"
+		sprite2_disabled="ModernDropDownArrowDisabled"
+		sprite2_pressed="ModernDropDownArrowHighlight"
+		buffer_zone="8"
+		dropdown_size="225"
+		minimum_visible_items="3"
+		sprite_list="GrayBackground"
+		sprite_list_overlay="BlackBorder"
+		sprite_selectarea="ModernDarkBox"
+		sprite_selectarea_overlay="ModernDarkBoxWhiteBorder"
+		textcolor_selected="white"
+		textcolor_disabled="140 140 140 255"
+		scrollbar="true"
+		scrollbar_style="ModernScrollBar"
+		sound_opened="audio/interface/ui/ui_button_click.ogg"
+		sound_closed="audio/interface/ui/ui_button_click.ogg"
+		sound_selected="audio/interface/ui/ui_button_click.ogg"
+	/>
+
 	<style name="resourceText"
 		textcolor="white"
 		font="sans-bold-stroke-14"
diff --git a/binaries/data/mods/public/shaders/glsl/common/debug_fragment.h b/binaries/data/mods/public/shaders/glsl/common/debug_fragment.h
new file mode 100644
index 0000000000..0936a2ef71
--- /dev/null
+++ b/binaries/data/mods/public/shaders/glsl/common/debug_fragment.h
@@ -0,0 +1,20 @@
+#ifndef INCLUDED_DEBUG_FRAGMENT
+#define INCLUDED_DEBUG_FRAGMENT
+
+#define RENDER_DEBUG_MODE_NONE 0
+#define RENDER_DEBUG_MODE_AO 1
+
+#ifndef RENDER_DEBUG_MODE
+#define RENDER_DEBUG_MODE RENDER_DEBUG_MODE_NONE
+#endif
+
+vec3 applyDebugColor(vec3 color, float ao)
+{
+#if RENDER_DEBUG_MODE == RENDER_DEBUG_MODE_AO
+	return vec3(ao);
+#else
+	return color;
+#endif
+}
+
+#endif // INCLUDED_DEBUG_FRAGMENT
diff --git a/binaries/data/mods/public/shaders/glsl/model_common.fs b/binaries/data/mods/public/shaders/glsl/model_common.fs
index 25b18a9c10..a56599de11 100644
--- a/binaries/data/mods/public/shaders/glsl/model_common.fs
+++ b/binaries/data/mods/public/shaders/glsl/model_common.fs
@@ -1,5 +1,6 @@
 #version 120
 
+#include "common/debug_fragment.h"
 #include "common/fog.h"
 #include "common/los_fragment.h"
 #include "common/shadows_fragment.h"
@@ -153,16 +154,15 @@ void main()
     specular.rgb = sunColor * specCol * pow(max(0.0, dot(normalize(normal), v_half)), specPow);
   #endif
 
-  vec3 color = (texdiffuse * sundiffuse + specular.rgb) * getShadow();
-  vec3 ambColor = texdiffuse * ambient;
-
   #if (USE_INSTANCING || USE_GPU_SKINNING) && USE_AO
-    vec3 ao = texture2D(aoTex, v_tex2).rrr;
-    ao = mix(vec3(1.0), ao * 2.0, effectSettings.w);
-    ambColor *= ao;
+    float ao = texture2D(aoTex, v_tex2).r;
+    ao = mix(1.0, ao * 2.0, effectSettings.w);
+  #else
+    float ao = 1.0;
   #endif
 
-  color += ambColor;
+  vec3 ambientColor = texdiffuse * ambient * ao;
+  vec3 color = (texdiffuse * sundiffuse + specular.rgb) * getShadow() + ambientColor;
 
   #if USE_SPECULAR_MAP && USE_SELF_LIGHT
     color = mix(texdiffuse, color, specular.a);
@@ -174,5 +174,7 @@ void main()
 
   color *= shadingColor;
 
+  color = applyDebugColor(color, ao);
+
   gl_FragColor.rgb = color;
 }
diff --git a/binaries/data/mods/public/shaders/glsl/model_water.fs b/binaries/data/mods/public/shaders/glsl/model_water.fs
index a14ba67182..0b9f6deb49 100644
--- a/binaries/data/mods/public/shaders/glsl/model_water.fs
+++ b/binaries/data/mods/public/shaders/glsl/model_water.fs
@@ -1,5 +1,6 @@
 #version 120
 
+#include "common/debug_fragment.h"
 #include "common/los_fragment.h"
 #include "common/shadows_fragment.h"
 
@@ -90,8 +91,9 @@ void main()
 #endif
 
 	vec3 color = mix(refrColor + 0.3*specular, reflColor + specular, fresShadow);
+	color *= getLOS();
 
-	gl_FragColor.rgb = color * getLOS();
+	gl_FragColor.rgb = applyDebugColor(color, 1.0);
 
 	// Make alpha vary based on both depth (so it blends with the shore) and view angle (make it
 	// become opaque faster at lower view angles so we can't look "underneath" the water plane)
diff --git a/binaries/data/mods/public/shaders/glsl/model_waterfall.fs b/binaries/data/mods/public/shaders/glsl/model_waterfall.fs
index e4f99a6443..fa250fe315 100644
--- a/binaries/data/mods/public/shaders/glsl/model_waterfall.fs
+++ b/binaries/data/mods/public/shaders/glsl/model_waterfall.fs
@@ -1,5 +1,6 @@
 #version 120
 
+#include "common/debug_fragment.h"
 #include "common/los_fragment.h"
 #include "common/shadows_fragment.h"
 
@@ -37,6 +38,6 @@ void main()
 
 	color *= getLOS();
 
-	gl_FragColor.rgb = color;
+	gl_FragColor.rgb = applyDebugColor(color, 1.0);
 	gl_FragColor.a = texdiffuse.a;
 }
diff --git a/binaries/data/mods/public/shaders/glsl/overlayline.fs b/binaries/data/mods/public/shaders/glsl/overlayline.fs
index 7a2703b9f5..14ea735dbd 100644
--- a/binaries/data/mods/public/shaders/glsl/overlayline.fs
+++ b/binaries/data/mods/public/shaders/glsl/overlayline.fs
@@ -1,5 +1,6 @@
 #version 120
 
+#include "common/debug_fragment.h"
 #include "common/los_fragment.h"
 
 uniform sampler2D baseTex;
@@ -29,5 +30,5 @@ void main()
 
     color *= getLOS();
 
-    gl_FragColor = vec4(color, alpha * base.a);
+    gl_FragColor = vec4(applyDebugColor(color, 1.0), alpha * base.a);
 }
diff --git a/binaries/data/mods/public/shaders/glsl/terrain_common.fs b/binaries/data/mods/public/shaders/glsl/terrain_common.fs
index c6a37513aa..04b53038d8 100644
--- a/binaries/data/mods/public/shaders/glsl/terrain_common.fs
+++ b/binaries/data/mods/public/shaders/glsl/terrain_common.fs
@@ -1,5 +1,6 @@
 #version 120
 
+#include "common/debug_fragment.h"
 #include "common/fog.h"
 #include "common/los_fragment.h"
 #include "common/shadows_fragment.h"
@@ -183,7 +184,7 @@ void main()
     color *= shadingColor;
   #endif
 
-  gl_FragColor.rgb = color;
+  gl_FragColor.rgb = applyDebugColor(color, 1.0);
 
   #if USE_GRASS
     gl_FragColor.a = tex.a;
diff --git a/source/ps/CStrInternStatic.h b/source/ps/CStrInternStatic.h
index cae4a9c619..2e3bf36689 100644
--- a/source/ps/CStrInternStatic.h
+++ b/source/ps/CStrInternStatic.h
@@ -56,6 +56,9 @@ X(MODE_SHADOWCAST)
 X(MODE_SILHOUETTEDISPLAY)
 X(MODE_SILHOUETTEOCCLUDER)
 X(MODE_WIREFRAME)
+X(RENDER_DEBUG_MODE)
+X(RENDER_DEBUG_MODE_AO)
+X(RENDER_DEBUG_MODE_NONE)
 X(SHADOWS_CASCADE_COUNT)
 X(SYS_HAS_ARB)
 X(SYS_HAS_GLSL)
diff --git a/source/renderer/Renderer.cpp b/source/renderer/Renderer.cpp
index 0b054ad571..87bce141b6 100644
--- a/source/renderer/Renderer.cpp
+++ b/source/renderer/Renderer.cpp
@@ -515,6 +515,9 @@ void CRenderer::ReloadShaders()
 #endif
 	}
 
+	m->globalContext.Add(str_RENDER_DEBUG_MODE,
+		RenderDebugModeEnum::ToString(g_RenderingOptions.GetRenderDebugMode()));
+
 	if (g_RenderingOptions.GetPreferGLSL() && g_RenderingOptions.GetFog())
 		m->globalContext.Add(str_USE_FOG, str_1);
 
diff --git a/source/renderer/RenderingOptions.cpp b/source/renderer/RenderingOptions.cpp
index 3890238e62..cb65568577 100644
--- a/source/renderer/RenderingOptions.cpp
+++ b/source/renderer/RenderingOptions.cpp
@@ -22,6 +22,7 @@
 #include "ps/CLogger.h"
 #include "ps/ConfigDB.h"
 #include "ps/CStr.h"
+#include "ps/CStrInternStatic.h"
 #include "renderer/Renderer.h"
 #include "renderer/PostprocManager.h"
 #include "renderer/ShadowMap.h"
@@ -74,6 +75,29 @@ CStr8 RenderPathEnum::ToString(RenderPath path)
 	return "default"; // Silence warning about reaching end of non-void function.
 }
 
+RenderDebugMode RenderDebugModeEnum::FromString(const CStr8& name)
+{
+	if (name == str_RENDER_DEBUG_MODE_NONE.c_str())
+		return RenderDebugMode::NONE;
+	if (name == str_RENDER_DEBUG_MODE_AO.c_str())
+		return RenderDebugMode::AO;
+
+	LOGWARNING("Unknown render debug mode %s", name.c_str());
+	return RenderDebugMode::NONE;
+}
+
+CStrIntern RenderDebugModeEnum::ToString(RenderDebugMode mode)
+{
+	switch (mode)
+	{
+	case RenderDebugMode::AO:
+		return str_RENDER_DEBUG_MODE_AO;
+	default:
+		break;
+	}
+	return str_RENDER_DEBUG_MODE_NONE;
+}
+
 CRenderingOptions::CRenderingOptions() : m_ConfigHooks(new ConfigHooks())
 {
 	m_RenderPath = RenderPath::DEFAULT;
@@ -243,10 +267,16 @@ void CRenderingOptions::SetPreferGLSL(bool value)
 	g_Renderer.RecomputeSystemShaderDefines();
 }
 
-
 void CRenderingOptions::SetRenderPath(RenderPath value)
 {
 	m_RenderPath = value;
 	if (CRenderer::IsInitialised())
 		g_Renderer.SetRenderPath(m_RenderPath);
 }
+
+void CRenderingOptions::SetRenderDebugMode(RenderDebugMode value)
+{
+	m_RenderDebugMode = value;
+	if (CRenderer::IsInitialised())
+		g_Renderer.MakeShadersDirty();
+}
diff --git a/source/renderer/RenderingOptions.h b/source/renderer/RenderingOptions.h
index 6905a4f9c1..bf842004e3 100644
--- a/source/renderer/RenderingOptions.h
+++ b/source/renderer/RenderingOptions.h
@@ -28,6 +28,7 @@
 #define INCLUDED_RENDERINGOPTIONS
 
 #include "ps/CStr.h"
+#include "ps/CStrIntern.h"
 
 class CRenderer;
 
@@ -50,6 +51,18 @@ struct RenderPathEnum
 	static CStr8 ToString(RenderPath);
 };
 
+enum class RenderDebugMode
+{
+	NONE,
+	AO
+};
+
+struct RenderDebugModeEnum
+{
+	static RenderDebugMode FromString(const CStr8& name);
+	static CStrIntern ToString(RenderDebugMode mode);
+};
+
 class CRenderingOptions
 {
 	// The renderer needs access to our private variables directly because capabilities have not yet been extracted
@@ -88,6 +101,8 @@ OPTION_CUSTOM_SETTER(NAME, TYPE); OPTION_GETTER(NAME, TYPE); OPTION_DEF(NAME, TY
 
 	OPTION_WITH_SIDE_EFFECT(RenderPath, RenderPath);
 
+	OPTION_WITH_SIDE_EFFECT(RenderDebugMode, RenderDebugMode);
+
 	OPTION(WaterEffects, bool);
 	OPTION(WaterFancyEffects, bool);
 	OPTION(WaterRealDepth, bool);
diff --git a/source/renderer/scripting/JSInterface_Renderer.cpp b/source/renderer/scripting/JSInterface_Renderer.cpp
index 5d83138a15..ce7908cdd9 100644
--- a/source/renderer/scripting/JSInterface_Renderer.cpp
+++ b/source/renderer/scripting/JSInterface_Renderer.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2020 Wildfire Games.
+/* Copyright (C) 2021 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -47,6 +47,16 @@ std::string GetRenderPath()
 	return RenderPathEnum::ToString(g_RenderingOptions.GetRenderPath());
 }
 
+std::string GetRenderDebugMode()
+{
+	return RenderDebugModeEnum::ToString(g_RenderingOptions.GetRenderDebugMode()).c_str();
+}
+
+void SetRenderDebugMode(const std::string& mode)
+{
+	g_RenderingOptions.SetRenderDebugMode(RenderDebugModeEnum::FromString(mode));
+}
+
 bool TextureExists(const std::wstring& filename)
 {
 	return g_Renderer.GetTextureManager().TextureExists(filename);
@@ -60,6 +70,8 @@ void RegisterScriptFunctions(const ScriptRequest& rq)
 {
 	ScriptFunction::Register<&GetRenderPath>(rq, "Renderer_GetRenderPath");
 	ScriptFunction::Register<&TextureExists>(rq, "TextureExists");
+	ScriptFunction::Register<&GetRenderDebugMode>(rq, "Renderer_GetRenderDebugMode");
+	ScriptFunction::Register<&SetRenderDebugMode>(rq, "Renderer_SetRenderDebugMode");
 	REGISTER_BOOLEAN_SCRIPT_SETTING(DisplayFrustum);
 	REGISTER_BOOLEAN_SCRIPT_SETTING(DisplayShadowsFrustum);
 }