Add {GL, GLContext}.getDefaultDrawBuffer() to complement getDefaultReadBuffer()

7 files changed, 103 insertions, 28 deletions

diff --git a/make/config/jogl/gl-impl-CustomJavaCode-common.java b/make/config/jogl/gl-impl-CustomJavaCode-common.java
index b764191e2..b1500adcf 100644
--- a/make/config/jogl/gl-impl-CustomJavaCode-common.java
+++ b/make/config/jogl/gl-impl-CustomJavaCode-common.java
@@ -124,6 +124,11 @@
     }
 
     @Override
+    public final int getDefaultDrawBuffer() {
+      return _context.getDefaultDrawBuffer();
+    }
+
+    @Override
     public final int getDefaultReadBuffer() {
       return _context.getDefaultReadBuffer();
     }
diff --git a/src/jogl/classes/com/jogamp/opengl/FBObject.java b/src/jogl/classes/com/jogamp/opengl/FBObject.java
index a559445c7..8f62c9952 100644
--- a/src/jogl/classes/com/jogamp/opengl/FBObject.java
+++ b/src/jogl/classes/com/jogamp/opengl/FBObject.java
@@ -2772,7 +2772,11 @@ public class FBObject {
     public final int getReadFramebuffer() {
         return 0 < samples ? ( null != samplingSink ? samplingSink.getReadFramebuffer() : 0 ) : fbName;
     }
+
+    public final int getDefaultDrawBuffer() { return GL.GL_COLOR_ATTACHMENT0; }
+
     public final int getDefaultReadBuffer() { return GL.GL_COLOR_ATTACHMENT0; }
+
     /** Return the number of attached {@link Colorbuffer}s */
     public final int getColorbufferCount() { return colorbufferCount; }
     /** Return the number of attached {@link TextureAttachment}s */
diff --git a/src/jogl/classes/com/jogamp/opengl/GLBase.java b/src/jogl/classes/com/jogamp/opengl/GLBase.java
index 0cbcbe40f..a2f22a4d4 100644
--- a/src/jogl/classes/com/jogamp/opengl/GLBase.java
+++ b/src/jogl/classes/com/jogamp/opengl/GLBase.java
@@ -648,31 +648,55 @@ public interface GLBase {
     */
    public int getDefaultReadFramebuffer();
 
-   /**
-    * Returns the default color buffer within the current bound
-    * {@link #getDefaultReadFramebuffer()}, i.e. GL_READ_FRAMEBUFFER,
-    * which will be used as the source for pixel reading commands,
-    * like {@link GL#glReadPixels(int, int, int, int, int, int, java.nio.Buffer) glReadPixels} etc.
-    * <p>
-    * For offscreen framebuffer objects this is {@link GL#GL_COLOR_ATTACHMENT0},
-    * otherwise this is {@link GL#GL_FRONT} for single buffer configurations
-    * and {@link GL#GL_BACK} for double buffer configurations.
-    * </p>
-    * <p>
-    * Note-1: Neither ES1 nor ES2 supports selecting the read buffer via glReadBuffer
-    * and {@link GL#GL_BACK} is the default.
-    * </p>
-    * <p>
-    * Note-2: ES3 only supports {@link GL#GL_BACK}, {@link GL#GL_NONE} or {@link GL#GL_COLOR_ATTACHMENT0}+i
-    * </p>
-    * <p>
-    * Note-3: See {@link com.jogamp.opengl.util.GLDrawableUtil#swapBuffersBeforeRead(GLCapabilitiesImmutable) swapBuffersBeforeRead}
-    * for read-pixels and swap-buffers implications.
-    * </p>
-    * <p>
-    * Calls {@link GLContext#getDefaultReadBuffer()}.
-    * </p>
-    */
-   public int getDefaultReadBuffer();
+  /**
+   * Returns the default color buffer within the current bound
+   * {@link #getDefaultReadFramebuffer()}, i.e. GL_READ_FRAMEBUFFER​,
+   * which will be used as the target (output) for (fragment shader) draw commands,
+   * settable via {@link GL2ES2#glDrawBuffers(int, int[], int)} or {@link GL2#glDrawBuffer(int)}.
+   * <p>
+   * For offscreen framebuffer objects this is {@link GL#GL_COLOR_ATTACHMENT0},
+   * otherwise this is {@link GL#GL_FRONT} for non-ES profile and single buffer configurations
+   * and {@link GL#GL_BACK} for double buffer configurations or ES profiles.
+   * </p>
+   * <p>
+   * Note-1: Neither ES1 nor ES2 supports selecting the draw buffer at all
+   * and {@link GL#GL_BACK} is the default.
+   * </p>
+   * <p>
+   * Note-2: ES3 only supports {@link GL#GL_BACK}, {@link GL#GL_NONE} or {@link GL#GL_COLOR_ATTACHMENT0}+i
+   * via {@link GL2ES2#glDrawBuffers(int, int[], int)}.
+   * </p>
+   * <p>
+   * Method is only thread-safe while context is {@link #makeCurrent() made current}.
+   * </p>
+   */
+  public int getDefaultDrawBuffer();
+
+  /**
+   * Returns the default color buffer within the current bound
+   * {@link #getDefaultReadFramebuffer()}, i.e. GL_READ_FRAMEBUFFER​,
+   * which will be used as the source for pixel reading commands,
+   * like {@link GL#glReadPixels(int, int, int, int, int, int, java.nio.Buffer) glReadPixels} etc.
+   * <p>
+   * For offscreen framebuffer objects this is {@link GL#GL_COLOR_ATTACHMENT0},
+   * otherwise this is {@link GL#GL_FRONT} for non-ES profile and single buffer configurations
+   * and {@link GL#GL_BACK} for double buffer configurations or ES profiles.
+   * </p>
+   * <p>
+   * Note-1: Neither ES1 nor ES2 supports selecting the read buffer via glReadBuffer
+   * and {@link GL#GL_BACK} is the default.
+   * </p>
+   * <p>
+   * Note-2: ES3 only supports {@link GL#GL_BACK}, {@link GL#GL_NONE} or {@link GL#GL_COLOR_ATTACHMENT0}+i
+   * </p>
+   * <p>
+   * Note-3: See {@link com.jogamp.opengl.util.GLDrawableUtil#swapBuffersBeforeRead(GLCapabilitiesImmutable) swapBuffersBeforeRead}
+   * for read-pixels and swap-buffers implications.
+   * </p>
+   * <p>
+   * Method is only thread-safe while context is {@link #makeCurrent() made current}.
+   * </p>
+   */
+  public int getDefaultReadBuffer();
 }
 
diff --git a/src/jogl/classes/com/jogamp/opengl/GLContext.java b/src/jogl/classes/com/jogamp/opengl/GLContext.java
index 4455633a1..470635a98 100644
--- a/src/jogl/classes/com/jogamp/opengl/GLContext.java
+++ b/src/jogl/classes/com/jogamp/opengl/GLContext.java
@@ -1367,12 +1367,36 @@ public abstract class GLContext {
   /**
    * Returns the default color buffer within the current bound
    * {@link #getDefaultReadFramebuffer()}, i.e. GL_READ_FRAMEBUFFER​,
+   * which will be used as the target (output) for (fragment shader) draw commands,
+   * settable via {@link GL2ES2#glDrawBuffers(int, int[], int)} or {@link GL2#glDrawBuffer(int)}.
+   * <p>
+   * For offscreen framebuffer objects this is {@link GL#GL_COLOR_ATTACHMENT0},
+   * otherwise this is {@link GL#GL_FRONT} for non-ES profile and single buffer configurations
+   * and {@link GL#GL_BACK} for double buffer configurations or ES profiles.
+   * </p>
+   * <p>
+   * Note-1: Neither ES1 nor ES2 supports selecting the draw buffer at all
+   * and {@link GL#GL_BACK} is the default.
+   * </p>
+   * <p>
+   * Note-2: ES3 only supports {@link GL#GL_BACK}, {@link GL#GL_NONE} or {@link GL#GL_COLOR_ATTACHMENT0}+i
+   * via {@link GL2ES2#glDrawBuffers(int, int[], int)}.
+   * </p>
+   * <p>
+   * Method is only thread-safe while context is {@link #makeCurrent() made current}.
+   * </p>
+   */
+  public abstract int getDefaultDrawBuffer();
+
+  /**
+   * Returns the default color buffer within the current bound
+   * {@link #getDefaultReadFramebuffer()}, i.e. GL_READ_FRAMEBUFFER​,
    * which will be used as the source for pixel reading commands,
    * like {@link GL#glReadPixels(int, int, int, int, int, int, java.nio.Buffer) glReadPixels} etc.
    * <p>
    * For offscreen framebuffer objects this is {@link GL#GL_COLOR_ATTACHMENT0},
-   * otherwise this is {@link GL#GL_FRONT} for single buffer configurations
-   * and {@link GL#GL_BACK} for double buffer configurations.
+   * otherwise this is {@link GL#GL_FRONT} for non-ES profile and single buffer configurations
+   * and {@link GL#GL_BACK} for double buffer configurations or ES profiles.
    * </p>
    * <p>
    * Note-1: Neither ES1 nor ES2 supports selecting the read buffer via glReadBuffer
diff --git a/src/jogl/classes/jogamp/opengl/GLContextImpl.java b/src/jogl/classes/jogamp/opengl/GLContextImpl.java
index 88b746df6..8154dec31 100644
--- a/src/jogl/classes/jogamp/opengl/GLContextImpl.java
+++ b/src/jogl/classes/jogamp/opengl/GLContextImpl.java
@@ -2938,6 +2938,8 @@ public abstract class GLContextImpl extends GLContext {
   @Override
   public final int getDefaultReadFramebuffer() { return drawable.getDefaultReadFramebuffer(); }
   @Override
+  public final int getDefaultDrawBuffer() { return drawable.getDefaultDrawBuffer(gl); }
+  @Override
   public final int getDefaultReadBuffer() { return drawable.getDefaultReadBuffer(gl, drawableRead != drawable); }
 
   //---------------------------------------------------------------------------
diff --git a/src/jogl/classes/jogamp/opengl/GLDrawableImpl.java b/src/jogl/classes/jogamp/opengl/GLDrawableImpl.java
index 98a0a0948..4e0f5eaca 100644
--- a/src/jogl/classes/jogamp/opengl/GLDrawableImpl.java
+++ b/src/jogl/classes/jogamp/opengl/GLDrawableImpl.java
@@ -257,6 +257,17 @@ public abstract class GLDrawableImpl implements GLDrawable {
   protected int getDefaultDrawFramebuffer() { return 0; }
   /** Callback for special implementations, allowing GLContext to fetch a custom default read framebuffer. Defaults to zero. */
   protected int getDefaultReadFramebuffer() { return 0; }
+
+  /** Callback for special implementations, allowing GLContext to fetch a custom default draw buffer of current framebuffer. */
+  protected int getDefaultDrawBuffer(final GL gl) {
+      if( gl.isGLES() || getChosenGLCapabilities().getDoubleBuffered() ) {
+          // Note-1: Neither ES1 nor ES2 supports selecting the read buffer via glDrawBuffer
+          // Note-2: ES3 only supports GL_BACK, GL_NONE or GL_COLOR_ATTACHMENT0+i
+          return GL.GL_BACK;
+      }
+      return GL.GL_FRONT;
+  }
+
   /** Callback for special implementations, allowing GLContext to fetch a custom default read buffer of current framebuffer. */
   protected int getDefaultReadBuffer(final GL gl, final boolean hasDedicatedDrawableRead) {
       if( gl.isGLES() || hasDedicatedDrawableRead || getChosenGLCapabilities().getDoubleBuffered() ) {
diff --git a/src/jogl/classes/jogamp/opengl/GLFBODrawableImpl.java b/src/jogl/classes/jogamp/opengl/GLFBODrawableImpl.java
index 8ec3c0dd9..2bc682324 100644
--- a/src/jogl/classes/jogamp/opengl/GLFBODrawableImpl.java
+++ b/src/jogl/classes/jogamp/opengl/GLFBODrawableImpl.java
@@ -411,6 +411,11 @@ public class GLFBODrawableImpl extends GLDrawableImpl implements GLFBODrawable {
     protected final int getDefaultReadFramebuffer() { return initialized ? fbos[fboIFront].getReadFramebuffer() : 0; }
 
     @Override
+    protected final int getDefaultDrawBuffer(final GL gl) {
+        return initialized ? fbos[fboIBack].getDefaultDrawBuffer() : GL.GL_COLOR_ATTACHMENT0 ;
+    }
+
+    @Override
     protected final int getDefaultReadBuffer(final GL gl, final boolean hasDedicatedDrawableRead) {
         return initialized ? fbos[fboIFront].getDefaultReadBuffer() : GL.GL_COLOR_ATTACHMENT0 ;
     }