GraphicsAdapter will inquire the external Framebuffer if any and will try to play nicely with it

tsvm_core/src/net/torvald/tsvm/FBM.kt

@@ -0,0 +1,29 @@
+package net.torvald.tsvm
+
+import com.badlogic.gdx.graphics.glutils.FrameBuffer
+import java.util.*
+
+/**
+ * Nested FBOs are just not a thing in GL!
+ *
+ * Created by minjaesong on 2018-07-03.
+ *
+ * @link https://stackoverflow.com/questions/25471727/libgdx-nested-framebuffer
+ */
+internal object FBM {
+    private val stack = Stack<FrameBuffer>()
+
+    fun begin(buffer: FrameBuffer) {
+        if (!stack.isEmpty()) {
+            stack.peek().end()
+        }
+        stack.push(buffer).begin()
+    }
+
+    fun end() {
+        stack.pop().end()
+        if (!stack.isEmpty()) {
+            stack.peek().begin()
+        }
+    }
+}

tsvm_core/src/net/torvald/tsvm/peripheral/CharacterLCDdisplay.kt

@@ -3,6 +3,7 @@ package net.torvald.tsvm.peripheral
 import com.badlogic.gdx.graphics.Color
 import com.badlogic.gdx.graphics.Texture
 import com.badlogic.gdx.graphics.g2d.SpriteBatch
+import com.badlogic.gdx.graphics.glutils.FrameBuffer
 import net.torvald.terrarum.modulecomputers.virtualcomputer.tvd.toUlong
 import net.torvald.tsvm.TsvmTextureRegionPack
 import net.torvald.tsvm.VM
@@ -29,16 +30,23 @@ class CharacterLCDdisplay(assetsRoot: String, vm: VM) : GraphicsAdapter(assetsRo
         }
     }*/
 
-    override fun render(delta: Float, batch: SpriteBatch, xoff: Float, yoff: Float, flipY: Boolean) {
+    override fun render(
+        delta: Float,
+        batch: SpriteBatch,
+        xoff: Float,
+        yoff: Float,
+        flipY: Boolean,
+        uiFBO: FrameBuffer?
+    ) {
         batch.shader = null
         batch.inUse {
             batch.color = Color.WHITE
             batch.draw(machine, xoff, yoff)
         }
         if (!flipY)
-            super.render(delta, batch, xoff+74, yoff+102, flipY)
+            super.render(delta, batch, xoff+74, yoff+102, flipY, uiFBO)
         else
-            super.render(delta, batch, xoff+74, yoff+72, flipY)
+            super.render(delta, batch, xoff+74, yoff+72, flipY, uiFBO)
 
         // draw BMS and RTC
         val batPerc = "89"

tsvm_core/src/net/torvald/tsvm/peripheral/GraphicsAdapter.kt

@@ -6,11 +6,10 @@ import com.badlogic.gdx.graphics.g2d.Gdx2DPixmap
 import com.badlogic.gdx.graphics.g2d.SpriteBatch
 import com.badlogic.gdx.graphics.g2d.TextureRegion
 import com.badlogic.gdx.graphics.glutils.FrameBuffer
-import com.badlogic.gdx.graphics.glutils.PixmapTextureData
 import com.badlogic.gdx.math.Matrix4
-import com.badlogic.gdx.utils.GdxRuntimeException
 import net.torvald.UnsafeHelper
 import net.torvald.terrarum.modulecomputers.virtualcomputer.tvd.toUint
+import net.torvald.tsvm.FBM
 import net.torvald.tsvm.LoadShader
 import net.torvald.tsvm.VM
 import net.torvald.tsvm.kB
@@ -710,7 +709,10 @@ open class GraphicsAdapter(private val assetsRoot: String, val vm: VM, val confi
         unusedArea[1].toInt().and(15).toFloat() / 15f,
         unusedArea[2].toInt().and(15).toFloat() / 15f, 1f)
 
-    open fun render(delta: Float, uiBatch: SpriteBatch, xoff: Float, yoff: Float, flipY: Boolean = false) {
+    open fun render(delta: Float, uiBatch: SpriteBatch, xoff: Float, yoff: Float, flipY: Boolean = false,  uiFBO: FrameBuffer? = null) {
+        uiFBO?.end()
+
+
         // must reset positions as pixmaps expect them to be zero
         framebuffer.pixels.position(0)
         chrrom.pixels.position(0)
@@ -880,6 +882,7 @@ open class GraphicsAdapter(private val assetsRoot: String, val vm: VM, val confi
                 outFBObatch.draw(outFBOregion[0], 0f, HEIGHT.toFloat(), WIDTH.toFloat(), -HEIGHT.toFloat())
             }
         }
+        uiFBO?.begin()
 
         uiBatch.inUse {
             uiBatch.shader = null
@@ -1753,9 +1756,9 @@ internal infix fun Int.fmod(other: Int): Int {
 }
 
 internal fun FrameBuffer.inUse(action: () -> Unit) {
-    this.begin()
+    FBM.begin(this)
     action()
-    this.end()
+    FBM.end()
 }
 
 internal fun SpriteBatch.inUse(action: () -> Unit) {

tsvm_core/src/net/torvald/tsvm/peripheral/TexticsAdapter.kt

@@ -4,6 +4,7 @@ import com.badlogic.gdx.graphics.Color
 import com.badlogic.gdx.graphics.GL20
 import com.badlogic.gdx.graphics.Texture
 import com.badlogic.gdx.graphics.g2d.SpriteBatch
+import com.badlogic.gdx.graphics.glutils.FrameBuffer
 import net.torvald.tsvm.VM
 import net.torvald.tsvm.kB
 import kotlin.math.absoluteValue
@@ -38,9 +39,16 @@ open class TexticsAdapterBase(assetsRoot: String, vm: VM, config: AdapterConfig)
     private val ALIGN = (HEIGHT - TEX_HEIGHT).absoluteValue / 2f
     private val phosphorCol = crtColor[theme.substring(4)] ?: crtColor["white"]
 
-    override fun render(delta: Float, batch: SpriteBatch, xoff: Float, yoff: Float, flipY: Boolean) {
+    override fun render(
+        delta: Float,
+        batch: SpriteBatch,
+        xoff: Float,
+        yoff: Float,
+        flipY: Boolean,
+        uiFBO: FrameBuffer?
+    ) {
 
-        super.render(delta, batch, xoff, yoff, flipY)
+        super.render(delta, batch, xoff, yoff, flipY, uiFBO)
 
         batch.inUse {
             batch.enableBlending()