Question

我只创建了像osx预览应用程序之类的应用程序。我使用opengl或metalkit渲染图像。我可以通过某个矩阵对中心点（0,0）进行缩放，但是由于不知道如何创建模型矩阵，因此无法使用触摸板像预览应用那样对两根手指之间的点进行缩放。

我只是在苹果开发论坛上问了我的问题，并在github上找到了演示，但没人能帮我。

- (void)magnifyWithEvent:(NSEvent *)event {
    NSPoint eventLocation = [event locationInWindow];
    NSPoint center = [self.view convertPoint:eventLocation fromView:nil];
    NSPoint openglCenter = CGPointMake(center.x / ([[[NSApplication sharedApplication] mainWindow] frame].size.width / 2.0) - 1.0, center.y / ([[[NSApplication sharedApplication] mainWindow] frame].size.height / 2.0) - 1.0);
    NSRect frame = [[[NSApplication sharedApplication] mainWindow] frame];

    if ([event magnification] > 0)
    {
        if ([self zoomValue] <= 2.0)
        {
            [self setZoomValue:[self zoomValue] + [event magnification]];
            if(self.zoomValue > 2.0) {
                return;
            }
            self.slider.floatValue = [self zoomValue];

            self.panMatrix = GLKMatrix4Translate(GLKMatrix4Identity, self.swipX / (frame.size.width / 2.0), -self.swipY / (frame.size.height / 2.0), 1);
            self.scaleMatrix = GLKMatrix4Scale(self.baseScaleMatrix, self.zoomValue, self.zoomValue, 1);
            GLKMatrix4 model = GLKMatrix4Multiply(self.panMatrix, self.scaleMatrix);
            [self.testView makeChangeWithMat:model];
        } else {
            [self setZoomValue:2.0];
            self.slider.floatValue = [self zoomValue];

            self.panMatrix = GLKMatrix4Translate(GLKMatrix4Identity, self.swipX / (frame.size.width / 2.0), -self.swipY / (frame.size.height / 2.0), 1);
            self.scaleMatrix = GLKMatrix4Scale(self.baseScaleMatrix, self.zoomValue, self.zoomValue, 1);
            GLKMatrix4 model = GLKMatrix4Multiply(self.panMatrix, self.scaleMatrix);
            [self.testView makeChangeWithMat:model];
        }
    }
    else if ([event magnification] < 0)
    {
        if ([self zoomValue] + [event magnification] >= 1.0)
        {
            [self setZoomValue:[self zoomValue] + [event magnification]];
            self.slider.floatValue = [self zoomValue];

            self.panMatrix = GLKMatrix4Translate(GLKMatrix4Identity, self.swipX / (frame.size.width / 2.0), -self.swipY / (frame.size.height / 2.0), 1);
            self.scaleMatrix = GLKMatrix4Scale(self.baseScaleMatrix, self.zoomValue, self.zoomValue, 1);
            GLKMatrix4 model = GLKMatrix4Multiply(self.panMatrix, self.scaleMatrix);
            [self.testView makeChangeWithMat:model];
        }
        else
        {
            [self setZoomValue:1.0];
            if(self.zoomValue < 1.0) {
                return;
            }
            self.slider.floatValue = [self zoomValue];

            self.panMatrix = GLKMatrix4Translate(GLKMatrix4Identity, self.swipX / (frame.size.width / 2.0), -self.swipY / (frame.size.height / 2.0), 1);
            self.scaleMatrix = GLKMatrix4Scale(self.baseScaleMatrix, self.zoomValue, self.zoomValue, 1);
            GLKMatrix4 model = GLKMatrix4Multiply(self.panMatrix, self.scaleMatrix);
            [self.testView makeChangeWithMat:model];
        }
    }
}

Answer 1

要缩放任意点，您需要：

平移（中心点），从而更改第2步的原点
按必要的比例缩放
平移-（center-point），从而将原点返回到（0,0）

您完全错过了其中一种翻译。您需要类似的东西：

NSPoint eventLocation = [event locationInWindow];
NSPoint center = [self.view convertPoint:eventLocation fromView:nil];

double transX = 1.0 - center.x / (frame.size.width / 2.0);
double transY = 1.0 - center.y / (frame.size.height / 2.0);
GLKMatrix4 trans = GLKMatrix4Translate(GLKMatrix4Identity, transX, transY, 0);
GLKMatrix4 transBack = GLKMatrix4Translate(GLKMatrix4Identity, -transX, -transY, 0);
GLKMatrix4 scaleMatrix = GLKMatrix4Scale(GLKMatrix4Identity, self.zoomValue, self.zoomValue, 1);
GLKMatrix4 model = GLKMatrix4Multiply( transBack, GLKMatrix4Multiply( GLKMatrix4Multiply( scaleMatrix, trans ), _baseScaleMatrix ) );

编辑：同样，您不能将投影矩阵（_baseScaleMatrix）混合到模型矩阵中，必须先应用投影，然后再应用模型矩阵。

使用触摸板放大一个点（使用缩放并使用Objective-C在opengl或metalkit中平移和旋转）

1 个答案: