objective-c - 从触摸点获取单个像素

Question

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 x-y 坐标？如何区分用户用拇指绘图和用指尖绘图的区别？我想根据用户触摸屏幕的方式反射(reflect)画笔的差异，并且还想跟踪所有被触摸的像素。

我目前正在使用 Apple 开发者网站的 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制并沿途跟踪 x-y 坐标。如何根据用户触摸屏幕的方式更改画笔并跟踪一段时间内触摸的所有像素？

// 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.

}

Answer 1

据我所知，没有 API 可以访问触摸区域进行触摸。考虑到电容式触摸屏的限制，我什至不确定您想要的东西在物理上是否可行。我记得最近在 Cocoa Heads 上的一次演示，其中演示了 OS X 上(通过私有(private) API)可用于触控板的一些信息，但不适用于 iOS。

我相信这是图形输入板采用内置传感器技术的特殊手写笔的原因之一。

对于绘图应用程序来说，部分解决方法可能是像某些桌面应用程序那样模拟“墨迹书写”:如果用户的触摸停留在给定位置，则进行绘制，就好像墨水从“笔”中流出并逐渐扩散一样通过“纸”。