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是否有可能检测到每个被触摸的像素？更具体地说，当用户触摸屏幕时，是否有可能跟踪用户触摸的点集群的所有x-y坐标？我如何分辨用户用拇指进行绘图时以及用手指尖进行绘制时的区别？我想根据用户触摸屏幕来反映画笔的差异，并且还想跟踪所有正在触摸的像素。从触摸点获取单个像素
我目前使用下面的代码从苹果开发者网站的GLPaint样本：
http://developer.apple.com/library/ios/#samplecode/GLPaint/Introduction/Intro.html
样本代码允许预定义的画笔大小绘制和跟踪沿途的X-Y坐标。如何根据用户触摸屏幕的方式更改画笔并随着时间的推移跟踪所有正在触摸的像素？
// 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.
}
非常感谢您的回复。你知道这是否可能在Android上？ – HappyAppDeveloper 2012-04-04 17:06:41
我不知道，对不起，我不为Android开发。不过，我确信其他人会有答案。如果您在搜索中找不到任何内容，我建议发布标记为Android的新问题。 – 2012-04-04 17:10:20