/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include "renderstate/TextureState.h"

#include "Caches.h"
#include "utils/TraceUtils.h"

#include <GLES3/gl3.h>
#include <memory>
#include <SkCanvas.h>
#include <SkBitmap.h>

namespace android {
namespace uirenderer {

// Width of mShadowLutTexture, defines how accurate the shadow alpha lookup table is
static const int SHADOW_LUT_SIZE = 128;

// Must define as many texture units as specified by kTextureUnitsCount
const GLenum kTextureUnits[] = {
    GL_TEXTURE0,
    GL_TEXTURE1,
    GL_TEXTURE2,
    GL_TEXTURE3
};

TextureState::TextureState()
        : mTextureUnit(0) {
    glActiveTexture(kTextureUnits[0]);
    resetBoundTextures();

    GLint maxTextureUnits;
    glGetIntegerv(GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS, &maxTextureUnits);
    LOG_ALWAYS_FATAL_IF(maxTextureUnits < kTextureUnitsCount,
            "At least %d texture units are required!", kTextureUnitsCount);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
}

TextureState::~TextureState() {
    if (mShadowLutTexture != nullptr) {
        mShadowLutTexture->deleteTexture();
    }
}

/**
 * Maps shadow geometry 'alpha' varying (1 for darkest, 0 for transparent) to
 * darkness at that spot. Input values of 0->1 should be mapped within the same
 * range, but can affect the curve for a different visual falloff.
 *
 * This is used to populate the shadow LUT texture for quick lookup in the
 * shadow shader.
 */
static float computeShadowOpacity(float ratio) {
    // exponential falloff function provided by UX
    float val = 1 - ratio;
    return exp(-val * val * 4.0) - 0.018;
}

void TextureState::constructTexture(Caches& caches) {
    if (mShadowLutTexture == nullptr) {
        mShadowLutTexture.reset(new Texture(caches));

        unsigned char bytes[SHADOW_LUT_SIZE];
        for (int i = 0; i < SHADOW_LUT_SIZE; i++) {
            float inputRatio = i / (SHADOW_LUT_SIZE - 1.0f);
            bytes[i] = computeShadowOpacity(inputRatio) * 255;
        }
        mShadowLutTexture->upload(GL_ALPHA, SHADOW_LUT_SIZE, 1, GL_ALPHA, GL_UNSIGNED_BYTE, &bytes);
        mShadowLutTexture->setFilter(GL_LINEAR);
        mShadowLutTexture->setWrap(GL_CLAMP_TO_EDGE);
    }
}

void TextureState::activateTexture(GLuint textureUnit) {
    LOG_ALWAYS_FATAL_IF(textureUnit >= kTextureUnitsCount,
            "Tried to use texture unit index %d, only %d exist",
            textureUnit, kTextureUnitsCount);
    if (mTextureUnit != textureUnit) {
        glActiveTexture(kTextureUnits[textureUnit]);
        mTextureUnit = textureUnit;
    }
}

void TextureState::resetActiveTexture() {
    mTextureUnit = -1;
}

void TextureState::bindTexture(GLuint texture) {
    if (mBoundTextures[mTextureUnit] != texture) {
        glBindTexture(GL_TEXTURE_2D, texture);
        mBoundTextures[mTextureUnit] = texture;
    }
}

void TextureState::bindTexture(GLenum target, GLuint texture) {
    if (target == GL_TEXTURE_2D) {
        bindTexture(texture);
    } else {
        // GLConsumer directly calls glBindTexture() with
        // target=GL_TEXTURE_EXTERNAL_OES, don't cache this target
        // since the cached state could be stale
        glBindTexture(target, texture);
    }
}

void TextureState::deleteTexture(GLuint texture) {
    // When glDeleteTextures() is called on a currently bound texture,
    // OpenGL ES specifies that the texture is then considered unbound
    // Consider the following series of calls:
    //
    // glGenTextures -> creates texture name 2
    // glBindTexture(2)
    // glDeleteTextures(2) -> 2 is now unbound
    // glGenTextures -> can return 2 again
    //
    // If we don't call glBindTexture(2) after the second glGenTextures
    // call, any texture operation will be performed on the default
    // texture (name=0)

    unbindTexture(texture);

    glDeleteTextures(1, &texture);
}

void TextureState::resetBoundTextures() {
    for (int i = 0; i < kTextureUnitsCount; i++) {
        mBoundTextures[i] = 0;
    }
}

void TextureState::unbindTexture(GLuint texture) {
    for (int i = 0; i < kTextureUnitsCount; i++) {
        if (mBoundTextures[i] == texture) {
            mBoundTextures[i] = 0;
        }
    }
}

} /* namespace uirenderer */
} /* namespace android */