/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
#include "GpuTimer.h"
#include "gl/SkGLContext.h"
#include "gl/GrGLUtil.h"

GpuTimer::GpuTimer(const SkGLContext* glctx) : fContext(glctx) {
    if (fContext) {
        fContext->ref();
        fContext->makeCurrent();
        fStarted = false;
        fSupported = GrGLGetVersion(fContext->gl()) > GR_GL_VER(3,3) ||
                fContext->gl()->hasExtension("GL_ARB_timer_query") ||
                fContext->gl()->hasExtension("GL_EXT_timer_query");

        if (fSupported) {
            SK_GL(*fContext, GenQueries(1, &fQuery));
        }
    }
}

GpuTimer::~GpuTimer() {
    if (fContext) {
        if (fSupported) {
            fContext->makeCurrent();
            SK_GL(*fContext, DeleteQueries(1, &fQuery));
        }
        fContext->unref();
    }
}

void GpuTimer::start() {
    if (fContext && fSupported) {
        fContext->makeCurrent();
        fStarted = true;
        SK_GL(*fContext, BeginQuery(GR_GL_TIME_ELAPSED, fQuery));
    }
}

/**
 * It is important to stop the cpu clocks first,
 * as this will cpu wait for the gpu to finish.
 */
double GpuTimer::end() {
    if (fContext && fSupported) {
        fStarted = false;
        fContext->makeCurrent();
        SK_GL(*fContext, EndQuery(GR_GL_TIME_ELAPSED));

        GrGLint available = 0;
        while (!available) {
            SK_GL_NOERRCHECK(*fContext, GetQueryObjectiv(fQuery,
                                                         GR_GL_QUERY_RESULT_AVAILABLE,
                                                         &available));
            // If GetQueryObjectiv is erroring out we need some alternative
            // means of breaking out of this loop
            GrGLenum error;
            SK_GL_RET_NOERRCHECK(*fContext, error, GetError());
            if (GR_GL_NO_ERROR != error) {
                break;
            }
        }
        GrGLuint64 totalGPUTimeElapsed = 0;
        SK_GL(*fContext, GetQueryObjectui64v(fQuery,
                                             GR_GL_QUERY_RESULT,
                                             &totalGPUTimeElapsed));

        return totalGPUTimeElapsed / 1000000.0;
    } else {
        return 0;
    }
}