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我對OpenGL非常陌生，我正在做一個非常簡單的程序來檢查我是否可以選擇在屏幕上呈現的對象，使用獨特的顏色繪製每個對象。到目前爲止，我呈現了2個平方和一個三角形。使用顏色在Android OpenGL ES中採摘對象無法檢索正確的顏色
問題是，當用戶觸摸多邊形時，我得到的顏色與黑色不同，但三個對象的顏色索引相同（當它應該不同時）。
這是我的代碼：
的onDrawFrame方法（我的渲染器內）。當用戶觸摸屏幕時，這裏是我用多種顏色渲染多邊形的地方。
public void onDrawFrame(GL10 gl) {
// clear Screen and Depth Buffer
gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
// Reset the Modelview Matrix
gl.glLoadIdentity();
if (mGLView.isPickingEnabled()) {
gl.glDisable(GL10.GL_TEXTURE_2D);
gl.glDisable(GL10.GL_LIGHTING);
gl.glDisable(GL10.GL_FOG);
// draw colored objects and picking pixel color
pickingDraw(gl);
mGLView.mPickingY = (int)(mHeight - mGLView.mPickingY);
gl.glReadPixels((int) mGLView.mPickingX,
(int) mGLView.mPickingY, 1, 1,
GL10.GL_RGBA,
GL10.GL_UNSIGNED_BYTE,
mGLView.m_PickingPixelBuffer);
Log.i("RA", "RGBA COLORS: " +
(int) mGLView.m_PickingPixelBuffer.get(0) + " , " +
(int) mGLView.m_PickingPixelBuffer.get(1) + " , " +
(int) mGLView.m_PickingPixelBuffer.get(2) + " , " +
(int) mGLView.m_PickingPixelBuffer.get(3));
mGLView.disablePicking();
// Clear BACK BUFFER
gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
}
gl.glLoadIdentity();
// Drawing
gl.glTranslatef(0.0f, 0.0f, -25.0f); // move 5 units INTO the screen
// is the same as moving the camera 5 units away
square.draw(gl); // Draw the triangle
gl.glTranslatef(0.0f, -5.0f, 0.0f);
square.draw(gl);
gl.glTranslatef(4.0f, 10.0f, 0.0f);
triangle.draw(gl);
}
pickingDraw方法如下（我的渲染中也是如此）：
private void pickingDraw(GL10 gl) {
// Drawing
gl.glTranslatef(0.0f, 0.0f, -25.0f); // move 5 units INTO the screen
gl.glColor4f(128, 0, 0, 1);
square.draw(gl); // Draw the triangle
gl.glTranslatef(0.0f, -5.0f, 0.0f);
gl.glColor4f(129, 0, 0, 1);
square.draw(gl);
gl.glTranslatef(4.0f, 10.0f, 0.0f);
gl.glColor4f(130, 0, 0, 1);
triangle.draw(gl);
}
在另一方面，我繼承GLSurfaceView這樣我就可以處理用戶觸摸。在這個班，我用這個方法：
public boolean onTouchEvent(MotionEvent e) {
float _iX = e.getX();
float _iY = e.getY();
int iIndex = -1;
int iRed;
m_PickingPixelBuffer = ByteBuffer.allocateDirect(4);
m_PickingPixelBuffer.order(ByteOrder.nativeOrder());
// setting globals for Renderer
mPickingX = _iX;
mPickingY = _iY;
mPickingEnabled = true;
requestRender();
// wait for picking process (renderer)
while(mPickingEnabled);
iRed = m_PickingPixelBuffer.get(0);
if(iRed < 0)
{
iRed += 256;
}
Log.i("RA", "Coordinates: (" + mPickingX + ", " + mPickingY + ")");
Log.i("RA", "Red Color " + iRed);
return true;
}
看來，它檢測到的平方，當我觸摸它們的三角形，但我得到了他們三個相同顏色的指標。另外，三個物體具有相同的顏色（我甚至分別繪製了紅色，綠色和藍色的值，它們具有相同的顏色，即最後一個繪製的顏色）。
最後，這是我的輸出得到，當我觸摸一個平方，然後一個空的空間，而另一方：
01-19 01:34:23.345: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:23.355: INFO/RA(11566): Coordinates: (247.81186, 391.0)
01-19 01:34:23.355: INFO/RA(11566): Red Color 255
01-19 01:34:23.385: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:23.385: INFO/RA(11566): Coordinates: (248.52428, 390.0)
01-19 01:34:23.385: INFO/RA(11566): Red Color 255
01-19 01:34:23.405: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:23.405: INFO/RA(11566): Coordinates: (248.52428, 390.0)
01-19 01:34:23.405: INFO/RA(11566): Red Color 255
01-19 01:34:24.305: INFO/RA(11566): RGBA COLORS: 0 , 0 , 0 , -1
01-19 01:34:24.315: INFO/RA(11566): Coordinates: (119.571884, 577.0)
01-19 01:34:24.315: INFO/RA(11566): Red Color 0
01-19 01:34:24.335: INFO/RA(11566): RGBA COLORS: 0 , 0 , 0 , -1
01-19 01:34:24.335: INFO/RA(11566): Coordinates: (119.33441, 573.0)
01-19 01:34:24.335: INFO/RA(11566): Red Color 0
01-19 01:34:24.355: INFO/RA(11566): RGBA COLORS: 0 , 0 , 0 , -1
01-19 01:34:24.355: INFO/RA(11566): Coordinates: (119.33441, 573.0)
01-19 01:34:24.355: INFO/RA(11566): Red Color 0
01-19 01:34:25.195: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:25.195: INFO/RA(11566): Coordinates: (259.80466, 395.0)
01-19 01:34:25.195: INFO/RA(11566): Red Color 255
01-19 01:34:25.215: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:25.215: INFO/RA(11566): Coordinates: (259.44843, 398.0)
01-19 01:34:25.215: INFO/RA(11566): Red Color 255
01-19 01:34:25.245: INFO/RA(11566): RGBA COLORS: -1 , 0 , 0 , -1
01-19 01:34:25.245: INFO/RA(11566): Coordinates: (259.80466, 395.0)
01-19 01:34:25.245: INFO/RA(11566): Red Color 255
我不知道爲什麼紅色值對每個對象相同。
任何幫助，將不勝感激。 謝謝。