前面有一篇探討了如何在片段着色器中將YUV數據轉換爲RGB數據並顯示,但採用samplerExternalOES將SurfaceTexture作爲OpenGL外部紋理,需要使用GL_TEXTURE_EXTERNAL_OES作爲紋理模板,通過SetPreviewTexture將Camera數據圖像輸出到SurfaceTexture,調用updateTexImage()時將對應紋理更新爲最新的一幀,然後通知OpenGL繪製對應紋理。
1.創建紋理ID
int[] texture = new int[1];
GLES20.glGenTextures(1, texture, 0);
GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, texture[0]);
GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES,
GL10.GL_TEXTURE_MIN_FILTER,GL10.GL_LINEAR);
GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES,
GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);
GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES,
GL10.GL_TEXTURE_WRAP_S, GL10.GL_CLAMP_TO_EDGE);
GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES,
GL10.GL_TEXTURE_WRAP_T, GL10.GL_CLAMP_TO_EDGE);
return texture[0];
2.根據紋理id創建SurfaceTexture
mSurfaceTexture = new SurfaceTexture(textureId);
mSurfaceTexture.setOnFrameAvailableListener(listener);
private OnFrameAvailableListener listener = new OnFrameAvailableListener() {
@Override
public void onFrameAvailable(SurfaceTexture surfaceTexture) {
// TODO Auto-generated method stub
mGlSurfaceView.requestRender();
}
};
3.更改Shader
頂點着色器與之前相比多了個textureTransform,用於接收SurfaceTexture變換矩陣,如果不需要也可以不蓋被vertext shader。
片段着色器需要增加#extension GL_OES_EGL_image_external : require,因爲第一步的紋理都綁定到GL_TEXTURE_EXTERNAL_OES
對應採樣方式由Samlpe2D更改成samplerExternalOES。
public static final String NO_FILTER_VERTEX_SHADER = "" +
"attribute vec4 position;\n" +
" attribute vec4 inputTextureCoordinate;\n" +
" \n" +
"uniform mat4 textureTransform;\n" +
"varying vec2 textureCoordinate;\n" +
" \n" +
" void main()\n" +
"{\n" +
"textureCoordinate = (textureTransform * inputTextureCoordinate).xy;\n" +
"gl_Position = position;\n" +
"}";
public static final String NO_FILTER_FRAGMENT_SHADER = "" +
"#extension GL_OES_EGL_image_external : require\n"+
"precision mediump float;" +
"varying vec2 textureCoordinate;\n" +
"uniform samplerExternalOES inputImageTexture;\n" +
" \n" +
"void main() {" +
" gl_FragColor = texture2D( inputImageTexture, textureCoordinate );\n" +
"}";
4.繪製
與之前採用glTexImage2D綁定2D圖像紋理不同,這裏通過GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, textureid);綁定外部紋理即可。
如果使用了SurfaceTexture變換矩陣,可採用glUniformMatrix4fv傳遞給Shader
採用片段着色器方案的時間消耗主要在數據轉移中,本方法的格式相關工作交給EGLImage處理,用到了Lock ANativeWindow。具體優劣尚未探討,如有經驗人士希望指點迷津。