add flag to check whether draw/readBuffer() functions are available

core/src/processing/opengl/PGL.java

@@ -959,7 +959,7 @@ public abstract class PGL {
 
   protected void saveFirstFrame() {
     firstFrame = allocateDirectIntBuffer(graphics.width * graphics.height);
-    readBuffer(BACK);
+    if (hasReadBuffer()) readBuffer(BACK);
     readPixelsImpl(0, 0, graphics.width, graphics.height, RGBA, UNSIGNED_BYTE, firstFrame);
   }
 
@@ -2188,6 +2188,24 @@ public abstract class PGL {
   }
 
 
+  protected boolean hasReadBuffer() {
+    int[] version = getGLVersion();
+    if (isES()) {
+      return version[0] >= 3;
+    }
+    return version[0] > 2;
+  }
+
+
+  protected boolean hasDrawBuffer() {
+    int[] version = getGLVersion();
+    if (isES()) {
+      return version[0] >= 3;
+    }
+    return version[0] > 2;
+  }
+
+
   protected int maxSamples() {
     intBuffer.rewind();
     getIntegerv(MAX_SAMPLES, intBuffer);

core/src/processing/opengl/PGraphicsOpenGL.java

@@ -117,6 +117,8 @@ public class PGraphicsOpenGL extends PGraphics {
   static public boolean packedDepthStencilSupported;
   static public boolean anisoSamplingSupported;
   static public boolean blendEqSupported;
+  static public boolean readBufferSupported;
+  static public boolean drawBufferSupported;
 
   /** Some hardware limits */
   static public int maxTextureSize;
@@ -1682,7 +1684,7 @@ public class PGraphicsOpenGL extends PGraphics {
     FrameBuffer fb = getCurrentFB();
     if (fb != null) {
       fb.bind();
-      pgl.drawBuffer(fb.getDefaultDrawBuffer());
+      if (drawBufferSupported) pgl.drawBuffer(fb.getDefaultDrawBuffer());
     }
   }
 
@@ -1757,9 +1759,9 @@ public class PGraphicsOpenGL extends PGraphics {
 
     // We read from/write to the draw buffer.
     if (op == OP_READ) {
-      pgl.readBuffer(getCurrentFB().getDefaultDrawBuffer());
+      if (readBufferSupported) pgl.readBuffer(getCurrentFB().getDefaultDrawBuffer());
     } else if (op == OP_WRITE) {
-      pgl.drawBuffer(getCurrentFB().getDefaultDrawBuffer());
+      if (drawBufferSupported) pgl.drawBuffer(getCurrentFB().getDefaultDrawBuffer());
     }
 
     pixelsOp = op;
@@ -1774,8 +1776,8 @@ public class PGraphicsOpenGL extends PGraphics {
     }
 
     // Restoring default read/draw buffer configuration.
-    pgl.readBuffer(getCurrentFB().getDefaultReadBuffer());
-    pgl.drawBuffer(getCurrentFB().getDefaultDrawBuffer());
+    if (readBufferSupported) pgl.readBuffer(getCurrentFB().getDefaultReadBuffer());
+    if (drawBufferSupported) pgl.drawBuffer(getCurrentFB().getDefaultDrawBuffer());
 
     pixelsOp = OP_NONE;
   }
@@ -6864,6 +6866,8 @@ public class PGraphicsOpenGL extends PGraphics {
     fboMultisampleSupported = pgl.hasFboMultisampleSupport();
     packedDepthStencilSupported = pgl.hasPackedDepthStencilSupport();
     anisoSamplingSupported = pgl.hasAnisoSamplingSupport();
+    readBufferSupported = pgl.hasReadBuffer();
+    drawBufferSupported = pgl.hasDrawBuffer();
 
     try {
       pgl.blendEquation(PGL.FUNC_ADD);

core/src/processing/opengl/PJOGL.java

@@ -295,7 +295,7 @@ public class PJOGL extends PGL {
       // https://www.opengl.org/wiki/Default_Framebuffer
       // so it is copied to the front texture of the FBO layer:
       if (pclearColor || 0 < pgeomCount || !sketch.isLooping()) {
-        readBuffer(FRONT);
+        if (hasReadBuffer()) readBuffer(FRONT);
       } else {
         // ...except when the previous frame has not been cleared and nothing was
         // rendered while looping. In this case the back buffer, which holds the
@@ -306,7 +306,7 @@ public class PJOGL extends PGL {
       bindFramebufferImpl(DRAW_FRAMEBUFFER, glColorFbo.get(0));
       framebufferTexture2D(FRAMEBUFFER, COLOR_ATTACHMENT0,
                            TEXTURE_2D, glColorTex.get(frontTex), 0);
-      drawBuffer(COLOR_ATTACHMENT0);
+      if (hasDrawBuffer()) drawBuffer(COLOR_ATTACHMENT0);
       blitFramebuffer(0, 0, fboWidth, fboHeight,
                       0, 0, fboWidth, fboHeight,
                       COLOR_BUFFER_BIT, NEAREST);