中文(繁體)
中文(繁體)
在PHP 的圖像處理擴展GD 中， 是一個非常實用的函數，它可以為圖像資源設置圖層效果，從而實現各種疊加、混合或者透明效果。本文將詳細解析它的使用方法和基礎操作。
函數原型：
<span><span>bool</span></span><span> </span><span><span class="function_ invoke__">imagelayereffect</span></span> <span>(resource</span> <span><span>$image</span></span> <span>,</span> <span><span>int</span></span><span> </span><span><span>$effect</span></span> <span>) </span><p>參數說明：</p><ul><li> <span class="fun">$image</span> ：需要設置圖層效果的圖像資源，通常由<span class="fun"><a href="/zh-tw/php/imagecreatetruecolor.html" target="_blank">imagecreatetruecolor()</a></span>或<span class="fun"><a href="/zh-tw/php/imagecreatefromjpeg.html" target="_blank">imagecreatefromjpeg()</a></span>等函數生成。</li><li> <span class="fun">$effect</span> ：圖層效果常量，可以使用GD 提供的多種效果，如：</li><ul><li> <span class="fun">IMG_EFFECT_REPLACE</span> ：默認效果，替換圖像像素。</li><li> <span class="fun">IMG_EFFECT_ALPHABLEND</span> ：混合模式，支持alpha 通道透明疊加。</li><li> <span class="fun">IMG_EFFECT_NORMAL</span> ：普通繪製模式。</li><li> <span class="fun">IMG_EFFECT_OVERLAY</span> ：覆蓋模式，用於高亮或陰影效果。</li></ul></ul><h2> <span><span>2</span></span> <span>. 基本使用示例</span><p>下面是一個簡單示例，展示如何給圖像設置圖層效果並繪製半透明矩形：</p><pre> <?php <span><span>// 創建一張空白圖像</span></span><span> </span><span><span>$img</span></span> <span>=</span> <span><span class="function_ invoke__">imagecreatetruecolor</span></span> <span>(</span> <span><span>400</span></span> <span>,</span> <span><span>300</span></span> <span>); </span><span><span>// 填充背景為白色</span></span><span> </span><span><span>$white</span></span> <span>=</span> <span><span class="function_ invoke__">imagecolorallocate</span></span> <span>(</span> <span><span>$img</span></span> <span>,</span> <span><span>255</span></span> <span>,</span> <span><span>255</span></span> <span>,</span> <span><span>255</span></span> <span>); </span><span><span class="function_ invoke__">imagefill</span></span> <span>(</span> <span><span>$img</span></span> <span>,</span> <span><span>0</span></span> <span>,</span> <span><span>0</span></span> <span>,</span> <span><span>$white</span></span> <span>); </span><span><span>// 設置圖層效果為ALPHABLEND</span></span><span> </span><span><span class="function_ invoke__">imagelayereffect</span></span> <span>(</span> <span><span>$img</span></span> <span>, IMG_EFFECT_ALPHABLEND); </span><span><span>// 分配半透明紅色</span></span><span> </span><span><span>$red</span></span> <span>=</span> <span><span class="function_ invoke__">imagecolorallocatealpha</span></span> <span>(</span> <span><span>$img</span></span> <span>,</span> <span><span>255</span></span> <span>,</span> <span><span>0</span></span> <span>,</span> <span><span>0</span></span> <span>,</span> <span><span>63</span></span> <span>); </span><span><span>// 繪製半透明矩形</span></span><span> </span><span><span class="function_ invoke__">imagefilledrectangle</span></span> <span>(</span> <span><span>$img</span></span> <span>,</span> <span><span>50</span></span> <span>,</span> <span><span>50</span></span> <span>,</span> <span><span>350</span></span> <span>,</span> <span><span>250</span></span> <span>,</span> <span><span>$red</span></span> <span>); </span><span><span>// 輸出圖像</span></span><span> </span><span><span class="function_ invoke__">header</span></span> <span>(</span> <span><span>'Content-Type: image/png'</span></span> <span>); </span><span><span class="function_ invoke__">imagepng</span></span> <span>(</span> <span><span>$img</span></span> <span>); </span><span><span class="function_ invoke__">imagedestroy</span></span> <span>(</span> <span><span>$img</span></span> <span>); ?> </span><p>執行結果會在白色背景上顯示一個半透明的紅色矩形，通過<span class="fun">IMG_EFFECT_ALPHABLEND</span>實現了透明疊加效果。</p><h2> <span><span>3</span></span> <span>. 多種圖層特效結合使用</span><p>在實際應用中，你可能需要同時使用不同的圖層效果。例如繪製文本或多圖疊加，可以先設置圖層為<span class="fun">IMG_EFFECT_NORMAL</span>繪製基礎元素，再切換到<span class="fun">IMG_EFFECT_ALPHABLEND</span>疊加半透明效果：</p><pre> <span><span class="function_ invoke__">imagelayereffect</span></span> <span>(</span> <span><span>$img</span></span> <span>, IMG_EFFECT_NORMAL); </span><span><span class="function_ invoke__">imagestring</span></span> <span>(</span> <span><span>$img</span></span> <span>,</span> <span><span>5</span></span> <span>,</span> <span><span>10</span></span> <span>,</span> <span><span>10</span></span> <span>,</span> <span><span>"Hello World"</span></span> <span>,</span> <span><span>$black</span></span> <span>); </span><span><span class="function_ invoke__">imagelayereffect</span></span> <span>(</span> <span><span>$img</span></span> <span>, IMG_EFFECT_ALPHABLEND); </span><span><span class="function_ invoke__">imagefilledrectangle</span></span> <span>(</span> <span><span>$img</span></span> <span>,</span> <span><span>20</span></span> <span>,</span> <span><span>50</span></span> <span>,</span> <span><span>200</span></span> <span>,</span> <span><span>150</span></span> <span>,</span> <span><span>$semiTransparentBlue</span></span> <span>); </span><p>通過靈活切換<span class="fun">imagelayereffect()</span>的參數，可以實現複雜的圖層操作和圖像特效。</p><h2> <span><span>4</span></span> <span>. 注意事項</span><ul><li>在使用<span class="fun">IMG_EFFECT_ALPHABLEND</span>時，確保圖像支持alpha 通道（通過<span class="fun"><a href="/zh-tw/php/imagesavealpha.html" target="_blank">imagesavealpha()</a></span>設置）。</li><li>不同的GD 版本可能對某些效果支持不完全，請結合官方文檔和實際測試。</li><li>圖層效果只對後續繪製操作有效，之前繪製的內容不會受影響。</li></ul><h2> <span><span>5</span></span> <span>. 總結</span><p><span class="fun">imagelayereffect()</span>是GD 擴展中實現圖層混合和透明疊加的關鍵函數。掌握它的用法可以輕鬆實現半透明矩形、文本疊加、圖片疊加等各種特效。關鍵在於理解每種效果常量的作用，並根據需求靈活切換。</p><p>通過本文的講解和示例，相信你可以快速上手圖像圖層特效的基礎操作，為你的PHP 圖像處理項目增添更多創意和表現力。</p></div></div>
