I am having trouble reading out from a buffer mapped with glMapBufferRange
If I simply put some data in a buffer
// Create input VBO and vertex format
int bufferLength = 5 * 4; //5 floats 4 bytes each
FloatBuffer data = ByteBuffer.allocateDirect(bufferLength)
.order(ByteOrder.nativeOrder()).asFloatBuffer();
float[] floatData = { 1.0f, 4.0f, 9.0f, 16.0f, 25.0f };
data.put(floatData).position(0);
Generate a Array Buffer in GL and fill it with the data
int[] vbo = new int[1];
GLES30.glGenBuffers(1, vbo, 0);
GLES30.glBindBuffer(GLES30.GL_ARRAY_BUFFER, vbo[0]);
GLES30.glBufferData(GLES30.GL_ARRAY_BUFFER, bufferLength, data, GLES30.GL_STATIC_DRAW);
MyGLRenderer.checkGlError(TAG + " glBufferData GL_ARRAY_BUFFER");
When I map the buffer using glMapBufferRange and read the results
Buffer mappedBuffer = GLES30.glMapBufferRange(GLES30 .GL_ARRAY_BUFFER,
0, bufferLength, GLES30.GL_MAP_READ_BIT);
if (mappedBuffer!=null){
FloatBuffer transformedBuffer = ((ByteBuffer) mappedBuffer).asFloatBuffer();
MyGLRenderer.checkGlError(TAG + " glMapBufferRange");
Log.d(TAG, String.format("pre-run input values = %f %f %f %f %f\n", transformedBuffer.get(),
transformedBuffer.get(), transformedBuffer.get(), transformedBuffer.get(), transformedBuffer.get()));
transformedBuffer.position(0);
}
GLES30.glUnmapBuffer(GLES30.GL_ARRAY_BUFFER);
The logcat reads all zeros
D/TransformFeedback﹕ pre-run input values = 0.000000 0.000000 0.000000 0.000000 0.000000
No other errors are generated and I am not really sure what else to check. I have tried GLES30.glCopyBufferSubData(GLES30.GL_ARRAY_BUFFER, GLES30.GL_COPY_READ_BUFFER, 0, 0, bufferLength); and mapping GL_COPY_READ_BUFFER and gotten the same results.
I am testing on a Nexus 6 which supports OpenGL ES 3.1 so this functionality should be present.
This question suggests removing the OPENGL_FORWARD_COMPAT hint in glfw, could there be something similar that needs to happen in MyGLSurfaceView?
