我找到了解决这个问题的办法。最好的方法似乎是使用自定义帧缓冲区对象并渲染到纹理。在问这个问题之前,我还没听说过这个,但它看起来是一个非常有用的工具,对于OpenGLer的工具包来说!
对于那些可能想做类似的事情的人,你的想法是创建一个FBO并附加一个纹理到它(而不是一个渲染缓冲)。然后,可以绑定此FBO并像其他任何FBO一样绘制到它,唯一的区别是图形在屏幕外呈现。然后,要显示纹理,只需绑定主FBO并将纹理绘制到它(使用四边形)。
所以在我的实现中,我使用了两个不同的FBO,每个FBO都有一个纹理-一个用于“保留”图像(用于徒手画),另一个用于“抓取”图像(用于临时画)。每次渲染帧时,我首先绘制一个背景纹理(在我的例子中,我只是使用了Texture2D类),然后绘制保留的纹理,最后绘制scratch纹理(如果需要)。绘制临时形状时,所有内容都将渲染为“刮痕”纹理,并且在每帧开始时清除该纹理。完成后,scratch纹理将被绘制到保留的纹理。
下面是一些可能对某些人有用的代码片段:
1) 创建帧缓冲区(这里我只展示了两个以节省空间!):
// ---------- DEFAULT FRAMEBUFFER ---------- //
// Create framebuffer.
glGenFramebuffersOES(1, &viewFramebuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
// Create renderbuffer.
glGenRenderbuffersOES(1, &viewRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
// Get renderbuffer storage and attach to framebuffer.
[context renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:layer];
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, viewRenderbuffer);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
// Check for completeness.
status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES);
if (status != GL_FRAMEBUFFER_COMPLETE_OES) {
NSLog(@"Failed to make complete framebuffer object %x", status);
return NO;
}
// Unbind framebuffer.
glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0);
// ---------- RETAINED FRAMEBUFFER ---------- //
// Create framebuffer.
glGenFramebuffersOES(1, &retainedFramebuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, retainedFramebuffer);
// Create the texture.
glColor4f(0.0f, 0.0f, 0.0f, 0.0f);
glGenTextures(1, &retainedTexture);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, retainedTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1024, 1024, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glBindTexture(GL_TEXTURE_2D, 0);
// Attach the texture as a renderbuffer.
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, retainedTexture, 0);
// Check for completeness.
status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES);
if (status != GL_FRAMEBUFFER_COMPLETE_OES) {
NSLog(@"Failed to make complete framebuffer object %x", status);
return NO;
}
// Unbind framebuffer.
glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0);
2) 绘制到“渲染到纹理”FBO:
// Ensure that we are drawing to the current context.
[EAGLContext setCurrentContext:context];
glBindFramebufferOES(GL_FRAMEBUFFER_OES, retainedFramebuffer);
glViewport(0, 0, 1024, 1024);
// DRAWING CODE HERE
3) 将各种纹理渲染到主FBO,并呈现:
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
glViewport(0, 0, backingWidth, backingHeight);
glClearColor(1.0f, 1.0f, 1.0f, 1.0f); // Clear to white.
glClear(GL_COLOR_BUFFER_BIT);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
[self drawBackgroundTexture];
[self drawRetainedTexture];
[self drawScratchTexture];
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];
例如,使用
[self drawRetainedTexture]
将使用以下代码:
// Bind the texture.
glBindTexture(GL_TEXTURE_2D, retainedTexture);
// Destination coords.
GLfloat retainedVertices[] = {
0.0, backingHeight, 0.0,
backingWidth, backingHeight, 0.0,
0.0, 0.0, 0.0,
backingWidth, 0.0, 0.0
};
// Source coords.
GLfloat retainedTexCoords[] = {
0.0, 1.0,
1.0, 1.0,
0.0, 0.0,
1.0, 0.0
};
// Draw the texture.
glVertexPointer(3, GL_FLOAT, 0, retainedVertices);
glTexCoordPointer(2, GL_FLOAT, 0, retainedTexCoords);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
// Unbind the texture.
glBindTexture(GL_TEXTURE_2D, 0);
很多代码,但我希望这能帮助别人。这确实让我难堪了一阵子!
