我遇到了一个问题，我不知道它的最佳做法是什么。我有一个向上移动的背景，实际上是“切片”移动到另一个，好像屏幕被水平分割成4-5个部分。我需要能够在背景中绘制一个洞（圆圈）（透视），在指定的位置，它将在每帧左右动态变化。
以下是我如何生成区域，我不认为那里存在很多问题：
// A 'zone' is simply the 'slice' of ground that moves upward. There's about 4 of
// them visible on screen at the same time, and they are automatically generated by
// a method irrelevant to the situation. Zones are Sprites.
// ---------
void LevelLayer::Zone::generate(LevelLayer *sender) {
// [...]
// Make a background for the zone
Sprite *background = this->generateBackgroundSprite();
background->setPosition(_contentSize.width / 2, _contentSize.height / 2);
this->addChild(background, 0);
}
这是 Zone :: generateBackgroundSprite（）方法：
// generates dynamically a new background texture
Sprite *LevelLayer::Zone::generateBackgroundSprite() {
RenderTexture *rt = RenderTexture::create(_contentSize.width, _contentSize.height);
rt->retain();
Color4B dirtColorByte = Color4B(/*initialize the color with bytes*/);
Color4F dirtColor(dirtColorByte);
rt->beginWithClear(dirtColor.r, dirtColor.g, dirtColor.b, dirtColor.a);
// [Nothing here yet, gotta learn OpenGL m8]
rt->end();
// ++++++++++++++++++++
// I'm just testing clipping node, it works but the FPS get significantly lower.
// If I lock them to 60, they get down to 30, and if I lock them there they get
// to 20 :(
// Also for the test I'm drawing a square since ClippingNode doesn't seem to
// like circles...
DrawNode *square = DrawNode::create();
Point squarePoints[4] = { Point(-20, -20), Point(20, -20), Point(20, 20), Point(-20, 20) };
square->drawPolygon(squarePoints, 4, Color4F::BLACK, 0.0f, Color4F(0, 0, 0, 0));
square->setPosition(0, 0);
// Make a stencil
Node *stencil = Node::create();
stencil->addChild(square);
// Create a clipping node with the prepared stencil
ClippingNode *clippingNode = ClippingNode::create(stencil);
clippingNode->setInverted(true);
clippingNode->addChild(rt);
Sprite *ret = Sprite::create();
ret->addChild(clippingNode);
rt->release();
return ret;
}
**
所以我问你们，在这种情况下你会做什么？我在做什么好主意？你会以另一种更具想象力的方式做到这一点吗？
PS这是我为iOS制作的一个小应用程序的重写（我想将它移植到Android），我在Objective-C版本中使用了MutableTextures（它正在运行）。我只是想看看是否有更好的方法使用RenderTexture，所以我可以使用OpenGL调用动态创建背景图像。
我编写了自己的简单片段着色器，它根据另一个纹理（蒙版）的可见部分“遮盖”纹理的可见部分（背景）。我有一系列的点可以确定我的圆圈在屏幕上的位置，在update方法中我将它们绘制到RenderTexture。然后我将生成的纹理用作我传递给着色器的蒙版。
这是我的着色器：
#ifdef GL_ES
precision mediump float;
#endif
varying vec2 v_texCoord;
uniform sampler2D u_texture;
uniform sampler2D u_alphaMaskTexture;
void main() {
float maskAlpha = texture2D(u_alphaMaskTexture, v_texCoord).a;
float texAlpha = texture2D(u_texture, v_texCoord).a;
float blendAlpha = (1.0 - maskAlpha) * texAlpha; // Show only where mask is not visible
vec3 texColor = texture2D(u_texture, v_texCoord).rgb;
gl_FragColor = vec4(texColor, blendAlpha);
return;
}
init方法：
bool HelloWorld::init() {
// [...]
Size visibleSize = Director::getInstance()->getVisibleSize();
// Load and cache the custom shader
this->loadCustomShader();
// 'generateBackgroundSlice()' creates a new RenderTexture and fills it with a
// color, nothing too complicated here so I won't copy-paste it in my edit
m_background = Sprite::createWithTexture(this->generateBackgroundSprite()->getSprite()->getTexture());
m_background->setPosition(visibleSize.width / 2, visibleSize.height / 2);
this->addChild(m_background);
m_background->setShaderProgram(ShaderCache::getInstance()->getProgram(Shader_AlphaMask_frag_key));
GLProgram *shader = m_background->getShaderProgram();
m_alphaMaskTextureUniformLocation = glGetUniformLocation(shader->getProgram(), "u_alphaMaskTexture");
glUniform1i(m_alphaMaskTextureUniformLocation, 1);
m_alphaMaskRender = RenderTexture::create(m_background->getContentSize().width,
m_background->getContentSize().height);
m_alphaMaskRender->retain();
// [...]
}
loadCustomShader方法：
void HelloWorld::loadCustomShader() {
// Load the content of the vertex and fragement shader
FileUtils *fileUtils = FileUtils::getInstance();
string vertexSource = ccPositionTextureA8Color_vert;
string fragmentSource = fileUtils->getStringFromFile(
fileUtils->fullPathForFilename("Shader_AlphaMask_frag.fsh"));
// Init a shader and add its attributes
GLProgram *shader = new GLProgram;
shader->initWithByteArrays(vertexSource.c_str(), fragmentSource.c_str());
shader->bindAttribLocation(GLProgram::ATTRIBUTE_NAME_POSITION, GLProgram::VERTEX_ATTRIB_POSITION);
shader->bindAttribLocation(GLProgram::ATTRIBUTE_NAME_TEX_COORD, GLProgram::VERTEX_ATTRIB_TEX_COORDS);
shader->link();
shader->updateUniforms();
ShaderCache::getInstance()->addProgram(shader, Shader_AlphaMask_frag_key);
// Trace OpenGL errors if any
CHECK_GL_ERROR_DEBUG();
}
更新方法：
void HelloWorld::update(float dt) {
// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
// Create the mask texture from the points in the m_circlePos array
GLProgram *shader = m_background->getShaderProgram();
m_alphaMaskRender->beginWithClear(0, 0, 0, 0); // Begin with transparent mask
for (vector<Point>::iterator it = m_circlePos.begin(); it != m_circlePos.end(); it++) {
// draw a circle on the mask
const float radius = 40;
const int resolution = 20;
Point circlePoints[resolution];
Point center = *it;
center = Director::getInstance()->convertToUI(center); // OpenGL has a weird coordinates system
float angle = 0;
for (int i = 0; i < resolution; i++) {
float x = (radius * cosf(angle)) + center.x;
float y = (radius * sinf(angle)) + center.y;
angle += (2 * M_PI) / resolution;
circlePoints[i] = Point(x, y);
}
DrawNode *circle = DrawNode::create();
circle->retain();
circle->drawPolygon(circlePoints, resolution, Color4F::BLACK, 0.0f, Color4F(0, 0, 0, 0));
circle->setPosition(Point::ZERO);
circle->visit();
circle->release();
}
m_alphaMaskRender->end();
Texture2D *alphaMaskTexture = m_alphaMaskRender->getSprite()->getTexture();
alphaMaskTexture->setAliasTexParameters(); // Disable linear interpolation
// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
shader->use();
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, alphaMaskTexture->getName());
glActiveTexture(GL_TEXTURE0);
}
答案 0 :(得分：2)
你可能想看的是帧缓冲器，我不太熟悉OpenGL的移动API，但我确信你应该可以访问framebuffers。
你可能想要尝试的一个想法是做第一遍，你将你想要在背景上设置为alpha的圆圈渲染成一个新的帧缓冲纹理，然后你可以使用这个纹理作为alpha贴图你传递你的背景。所以基本上当渲染圆圈时，你可以将纹理中的值设置为0.0，对于alpha通道，否则为1.0，渲染时可以将片段的alpha通道设置为与第一遍的纹理alpha相同的值'渲染过程。
您可以将其视为与面具相同的想法。但只是使用另一种纹理。
希望这会有所帮助：）