经过一段时间的学习，我发现OpenGL是不支持字符绘制的，就是官方的API没有字符绘制的方法。但是如果有字符绘制的需求，还是有别的办法来实现，那就是把字符转换成图片，然后通过渲染纹理的方式把图片绘制出来。老规矩，先上效果图：
顶点shader：
uniform mat4 vMatrix;
attribute vec4 vPosition;
attribute vec2 vTextureCoordinate;
varying vec2 aTextureCoordinate;
void main() {
aTextureCoordinate = vTextureCoordinate;
gl_Position = vMatrix * vPosition;
}
片段shader：
precision mediump float;
uniform sampler2D u_TextureUnit;
varying vec2 aTextureCoordinate;
void main() {
gl_FragColor = texture2D(u_TextureUnit, aTextureCoordinate);
}
模型绘制类：
public class TextureModel {
private int programId;
private float[] matrix = new float[16];
private int glHMatrix;
private int glHPosition;
private int glHCoordinates;
private int glHTexture;
private FloatBuffer bufPos;
private FloatBuffer bufCoord;
private Bitmap bitmap;
private int[] textureId = new int[1];
private final float[] sCoord = { 0.0f, 0.0f, 0f, 0.0f, 1.0f, 0f, 1.0f, 0.0f, 0f, 1.0f, 1.0f, 0f };
public TextureModel(){
Matrix.setIdentityM(matrix, 0);
bufCoord = GlUtil.createFloatBuffer(sCoord);
}
public float[] getMatrix() { return matrix; }
public void createProgram(){
programId = GlUtil.createProgram(ResReadUtils.readResource(R.raw.texture_vertex_shader), ResReadUtils.readResource(R.raw.texture_fragment_shader));
glHMatrix = GLES20.glGetUniformLocation(programId, "vMatrix");
glHPosition = GLES20.glGetAttribLocation(programId, "vPosition");
glHCoordinates = GLES20.glGetAttribLocation(programId, "vTextureCoordinate");
glHTexture = GLES20.glGetUniformLocation(programId, "u_TextureUnit");
}
public void setBitmap(Bitmap bitmap) { this.bitmap = bitmap; }
public void createTexture(){
if (bitmap!=null && !bitmap.isRecycled()) {
GLES20.glGenTextures(1, textureId, 0);
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureId[0]);
GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR_MIPMAP_LINEAR);
GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR_MIPMAP_LINEAR);
GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S, GLES20.GL_CLAMP_TO_EDGE);
GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T, GLES20.GL_CLAMP_TO_EDGE);
GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, bitmap, 0);
GLES20.glGenerateMipmap(GLES20.GL_TEXTURE_2D);
bitmap.recycle();
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
}
}
public void setDrawPosition(float[] position){
if (position==null || position.length!=12) { return; }
bufPos = GlUtil.createFloatBuffer(position);
}
public void deleteTexture(){
GLES20.glDeleteTextures(programId, textureId, 0);
}
public void drawSelf(){
GLES20.glUseProgram(programId);
GLES20.glUniformMatrix4fv(glHMatrix, 1, false, matrix, 0);
GLES20.glEnableVertexAttribArray(glHPosition);
GLES20.glEnableVertexAttribArray(glHCoordinates);
GLES20.glUniform1i(glHTexture, 0);
createTexture();
GLES20.glVertexAttribPointer(glHPosition, 3, GLES20.GL_FLOAT, false, 0, bufPos);
GLES20.glVertexAttribPointer(glHCoordinates, 3, GLES20.GL_FLOAT, false, 0, bufCoord);
GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureId[0]);
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
GLES20.glDisableVertexAttribArray(glHPosition);
GLES20.glDisableVertexAttribArray(glHCoordinates);
}
现在需要传入字符的图片和坐标位置：
Paint paint =new Paint();
paint.setAntiAlias(true);
paint.setColor(Color.RED);
paint.setStyle(Paint.Style.FILL);
paint.setTextSize(100f);
String text ="测试字符串！";
int textWidth = (int) paint.measureText(text, 0, text.length());
Paint.FontMetrics fm = paint.getFontMetrics();
float textHeight = fm.bottom - fm.top + fm.leading;;
Bitmap bitmap = Bitmap.createBitmap(textWidth, (int)textHeight, Bitmap.Config.ARGB_8888);
Canvas canvas =new Canvas(bitmap);
canvas.drawText(text, 0, textHeight-fm.bottom, paint);
glSurfaceView.setTexture(bitmap);
RenderFilter调用方法：
public void setTextureBitmap(Bitmap bitmap){
float[] pos = {
0f, 0f, 10f,
0f, 0f, 0f,
0f, 10f, 10f,
0f, 10f, 0f
};
textureModel.setDrawPosition(pos);
textureModel.setBitmap(bitmap);
}
运行起来看看效果：
咦？怎么是白底的呢，难道生成的位图就是白底的？打个断点看看
从断点来看，生成的bitmap是透明的啊？？？那肯定是OpenGLES绘制的问题，为什么透明的绘制不出来，变成了白色的呢？
于是，百度一下，还真找到问题了：Android 使用opengles 设置背景透明
在onSurfaceCreated方法增加两行代码就搞定！
@Override
public void onSurfaceCreated(GL10 gl, EGLConfig config) {
GLES20.glEnable(GLES20.GL_DEPTH_TEST);
//就是下面这两行
GLES20.glEnable(GLES20.GL_BLEND);
GLES20.glBlendFunc(GLES20.GL_SRC_ALPHA, GLES20.GL_ONE_MINUS_SRC_ALPHA);
renderFilter.createProgram();
}
再运行起来看看效果，OK，收工！！！
