是否可以检测到每个被触摸的像素？更具体地说，当用户触摸屏幕时，是否可以跟踪用户触摸的点簇的所有 xy 坐标？我如何区分用户何时用拇指绘图和何时用指尖绘图？我想根据用户触摸屏幕的方式来反映画笔差异，并且还想跟踪所有被触摸的像素。
我目前正在使用来自 Apple 开发人员网站的 GLPaint 示例中的以下代码：
http://developer.apple.com/library/ios/#samplecode/GLPaint/Introduction/Intro.html
示例代码允许使用预定义的画笔大小进行绘图并沿途跟踪 xy 坐标。如何根据用户触摸屏幕的方式更改画笔并跟踪所有被触摸的像素？
// Drawings a line onscreen based on where the user touches
- (void) renderLineFromPoint:(CGPoint)start toPoint:(CGPoint)end
{
NSLog(@"x:%f y:%f",start.x, start.y);
static GLfloat* vertexBuffer = NULL;
static NSUInteger vertexMax = 64;
NSUInteger vertexCount = 0,
count,
i;
[EAGLContext setCurrentContext:context];
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
// Convert locations from Points to Pixels
CGFloat scale = self.contentScaleFactor;
start.x *= scale;
start.y *= scale;
end.x *= scale;
end.y *= scale;
// Allocate vertex array buffer
if(vertexBuffer == NULL)
vertexBuffer = malloc(vertexMax * 2 * sizeof(GLfloat));
// Add points to the buffer so there are drawing points every X pixels
count = MAX(ceilf(sqrtf((end.x - start.x) * (end.x - start.x) + (end.y - start.y) * (end.y - start.y)) / kBrushPixelStep), 1);
for(i = 0; i < count; ++i) {
if(vertexCount == vertexMax) {
vertexMax = 2 * vertexMax;
vertexBuffer = realloc(vertexBuffer, vertexMax * 2 * sizeof(GLfloat));
}
vertexBuffer[2 * vertexCount + 0] = start.x + (end.x - start.x) * ((GLfloat)i / (GLfloat)count);
vertexBuffer[2 * vertexCount + 1] = start.y + (end.y - start.y) * ((GLfloat)i / (GLfloat)count);
vertexCount += 1;
}
// Render the vertex array
glVertexPointer(2, GL_FLOAT, 0, vertexBuffer);
glDrawArrays(GL_POINTS, 0, vertexCount);
// Display the buffer
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];
}
// Handles the start of a touch
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
CGRect bounds = [self bounds];
UITouch* touch = [[event touchesForView:self] anyObject];
firstTouch = YES;
// Convert touch point from UIView referential to OpenGL one (upside-down flip)
location = [touch locationInView:self];
location.y = bounds.size.height - location.y;
}
// Handles the continuation of a touch.
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
CGRect bounds = [self bounds];
UITouch* touch = [[event touchesForView:self] anyObject];
// Convert touch point from UIView referential to OpenGL one (upside-down flip)
if (firstTouch) {
firstTouch = NO;
previousLocation = [touch previousLocationInView:self];
previousLocation.y = bounds.size.height - previousLocation.y;
} else {
location = [touch locationInView:self];
location.y = bounds.size.height - location.y;
previousLocation = [touch previousLocationInView:self];
previousLocation.y = bounds.size.height - previousLocation.y;
}
// Render the stroke
[self renderLineFromPoint:previousLocation toPoint:location];
}
// Handles the end of a touch event when the touch is a tap.
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
CGRect bounds = [self bounds];
UITouch* touch = [[event touchesForView:self] anyObject];
if (firstTouch) {
firstTouch = NO;
previousLocation = [touch previousLocationInView:self];
previousLocation.y = bounds.size.height - previousLocation.y;
[self renderLineFromPoint:previousLocation toPoint:location];
}
}
// Handles the end of a touch event.
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
// If appropriate, add code necessary to save the state of the application.
// This application is not saving state.
}