Customize rendering quality

[EJV96]

This is the best implementation of PDFRender I have seen so far. Excellent work, thanks for sharing it with everyone. The only flaw I see is that when you zoom in, the image quality is very poor. Is there a possibility of scaling the resolution while zooming in?

[barnhill]

Potentially... Any help is appreciated to make this better!

[barnhill]

This is potentially addressed in #11. I will take a look at this pull request and test it out. Thank you for contributing!

[EJV96]

This is potentially addressed in #11. I will take a look at this pull request and test it out. Thank you for contributing!

Scalability of quality as you zoom is not yet implemented, I tried different approaches but did not get the expected results. It seems that the way forward is to use a tile system, where only the visible part is rendered at the best quality. This is possible to do using PDFRenderer's Rect and Matrix parameters when rendering a page. What would need to be done is to couple the current Zoom implementation with a tile system and thus only render the visible sections of the page. Perhaps in the future I can spend more time on this and achieve a result more similar to what Adobe Acrobat does.

[mengsr]

我的项目中需要再比较小的父控件内显示文件，会导致放大失真效果严重，
fun generatePageBitmap(pageIndex: Int, size: IntSize): Bitmap? = pdf.openPage(pageIndex).use {
val widthMultiplier = (size.width.toFloat() / it.width.toFloat())

    val width = (it.width * maxOf(widthMultiplier, 1.1f)).toInt()
    val height = (it.height * maxOf(widthMultiplier, 1.1f)).toInt()

我觉得这样可能会稍微好点

[barnhill]

Oh let me try this out!! Thanks for your comment and I'll take a look a little later today.

[barnhill]

@EJV96 Sounds like you have a plan. Would you be willing to put a pull request together? PDFs are a pain and thats why I wanted to create this project is to get the community involved and pull together some great people to solve this for all of us.

[mengsr]

package com.pnuema.android.pdfviewer.generator

import android.graphics.Bitmap
import android.graphics.Matrix
import android.graphics.Rect
import android.graphics.pdf.PdfRenderer
import android.os.ParcelFileDescriptor
import android.util.Log
import androidx.annotation.WorkerThread
import androidx.compose.ui.unit.IntSize
import androidx.core.graphics.createBitmap
import java.io.Closeable
import java.io.File
import kotlin.math.max
import kotlin.math.min
import kotlin.system.measureTimeMillis

class PdfBitmapGenerator @workerthread constructor(file: File) : Closeable {
private val cache = PdfPageCache()
private val pdf = PdfRenderer(
ParcelFileDescriptor.open(
file,
ParcelFileDescriptor.MODE_READ_ONLY
)
)
val pageCount: Int get() = pdf.pageCount

init {
    Log.d("PdfViewer", "Generator created")
}

fun getPdfBitmap(pageIndex: Int, size: IntSize): Bitmap? = cache.get(pageIndex) ?: run {
    return@run generatePageBitmap(pageIndex, size)?.also {
        cache.put(pageIndex, it)
    }
}

fun generatePageBitmap(pageIndex: Int, size: IntSize): Bitmap? = pdf.openPage(pageIndex).use { page ->
    // 计算保持宽高比的缩放比例
    val pageWidth = page.width.toFloat()
    val pageHeight = page.height.toFloat()
    val targetWidth = size.width.toFloat()
    val targetHeight = size.height.toFloat()

    // 计算保持宽高比的最佳缩放比例
    val widthScale = targetWidth / pageWidth
    val heightScale = targetHeight / pageHeight

    // 使用较小的缩放比例确保图片完全显示（Fit模式）
    val scale = min(widthScale, heightScale)

    // 提高质量：使用至少3倍缩放保证清晰度
    val finalScale = max(scale, 3f)

    // 计算渲染尺寸
    val renderWidth = (pageWidth * finalScale).toInt()
    val renderHeight = (pageHeight * finalScale).toInt()

    if (renderWidth <= 0 || renderHeight <= 0) {
        Log.w("PdfViewer", "Invalid dimensions for page $pageIndex: ${renderWidth}x$renderHeight")
        return@use null
    }

    // 限制最大尺寸避免OOM
    val maxDimension = 6144
    val finalWidth = min(renderWidth, maxDimension)
    val finalHeight = min(renderHeight, maxDimension)

    // 计算实际使用的缩放比例（如果尺寸被限制）
    val actualScale = finalWidth.toFloat() / pageWidth

    try {
        val pdfPageBitmap = createBitmap(finalWidth, finalHeight, Bitmap.Config.ARGB_8888)

        val time = measureTimeMillis {
            // 关键：正确设置变换矩阵
            val matrix = Matrix().apply {
                postScale(actualScale, actualScale)
            }

            // 使用高质量的渲染模式
            val renderMode = if (actualScale >= 2.0f) {
                PdfRenderer.Page.RENDER_MODE_FOR_PRINT
            } else {
                PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY
            }

            // 渲染整个页面
            page.render(pdfPageBitmap, null, matrix, renderMode)
        }

        Log.d("PdfViewer", "Generated page $pageIndex (${finalWidth}x$finalHeight) in ${time}ms")
        pdfPageBitmap

    } catch (e: OutOfMemoryError) {
        Log.e("PdfViewer", "Out of memory generating page $pageIndex: ${e.message}")
        null
    } catch (e: Exception) {
        Log.e("PdfViewer", "Generating failed for page $pageIndex: ${e.message}")
        null
    }
}

/**
 * 新增：专门用于填充显示的方法（可能会裁剪部分内容）
 */
fun generatePageBitmapFill(pageIndex: Int, size: IntSize, crop: Boolean = true): Bitmap? =
    pdf.openPage(pageIndex).use { page ->
        val pageWidth = page.width.toFloat()
        val pageHeight = page.height.toFloat()
        val targetWidth = size.width.toFloat()
        val targetHeight = size.height.toFloat()

        // 计算填充整个区域的缩放比例（使用较大的比例）
        val widthScale = targetWidth / pageWidth
        val heightScale = targetHeight / pageHeight
        val scale = max(widthScale, heightScale)

        // 提高质量：使用至少2.0倍缩放保证清晰度
        val finalScale = max(scale, 2.0f)

        val renderWidth = (pageWidth * finalScale).toInt()
        val renderHeight = (pageHeight * finalScale).toInt()

        if (renderWidth <= 0 || renderHeight <= 0) return@use null

        try {
            val bitmap = createBitmap(renderWidth, renderHeight, Bitmap.Config.ARGB_8888)
            val matrix = Matrix().apply {
                postScale(finalScale, finalScale)
            }

            // 如果需要裁剪，先渲染完整页面再处理
            page.render(bitmap, null, matrix, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY)

            // 如果crop为true，裁剪到目标尺寸
            return@use if (crop && (renderWidth > size.width || renderHeight > size.height)) {
                val cropX = if (renderWidth > size.width) (renderWidth - size.width) / 2 else 0
                val cropY = if (renderHeight > size.height) (renderHeight - size.height) / 2 else 0

                Bitmap.createBitmap(
                    bitmap,
                    cropX,
                    cropY,
                    min(size.width, renderWidth),
                    min(size.height, renderHeight)
                ).also {
                    if (it != bitmap) {
                        bitmap.recycle()
                    }
                }
            } else {
                bitmap
            }

        } catch (e: Exception) {
            Log.e("PdfViewer", "Error in fill mode: ${e.message}")
            null
        }
    }

/**
 * 新增：保持原始比例的高质量渲染
 */
fun generateOriginalPageBitmap(pageIndex: Int, qualityScale: Float = 2.0f): Bitmap? =
    pdf.openPage(pageIndex).use { page ->
        val width = (page.width * qualityScale).toInt()
        val height = (page.height * qualityScale).toInt()

        if (width <= 0 || height <= 0) return@use null

        try {
            val bitmap = createBitmap(width, height, Bitmap.Config.ARGB_8888)
            val matrix = Matrix().apply {
                postScale(qualityScale, qualityScale)
            }

            page.render(bitmap, null, matrix, PdfRenderer.Page.RENDER_MODE_FOR_PRINT)
            bitmap
        } catch (e: Exception) {
            Log.e("PdfViewer", "Error in original mode: ${e.message}")
            null
        }
    }

override fun close() {
    pdf.close()

// cache.clear()
Log.d("PdfViewer", "Generator closed")
}
}