Drawing and scaling

Daniel Stefanescu posted an article and code that demonstrates drawing a line chart. I understand most of what is going on. I am stumped by the scaling code. Here is that snippet. XScale = (myRect.Width / (this.chartData.XValues.Length - 1)); a = (myRect.Height / (YMax - YMin)); b = -YMin * a; YScale = (myRect.Height / YMax); for (i = 0; i < this.chartData.XValues.Length; i++) { myX = XScale * i; myY = myRect.Height - (a * line.Values[i] + b); LinePoints[i] = new PointF(myX, myY); } myGraphics.DrawLines(LinePen, LinePoints); The entire article is titled "A Variety of Chart Engines". I changed two of the object names to make them more meaningful to me and removed some spaces. Other than that, the code is the same as in the article. Could someone explain the point of this code? How does this create the image to the appropriate size? I am guessing that's what it does.

I'm sure his intentions are good but its too many calculations for something extremely simple. YMin is the bottom of the grid and YMax is the top. a is the actual width in pixels of each grid and YScale is the yaxis width YScale: dont even bother with YScale its not used b is the actual distance to offset the y lines so then he just iterates through the points on the chart grid and plots them out according to its coordinates and draws a line I made one in jave for a 2d applet that auto scales and sizes based on tons of different variations and if you hacked at the code, organized it and gave meaningful names you could triple its effeciency. If you could come of with an algorithm to use bit shifting as opposed to multiplication you could handle larger loads. Multiplying is so over bearing on a cpu. its easy though you have a client grid area rectangle. thats your x and y. determine where the grid axis is based on use those variables to calculate based on a 0 base axis. then when you have the coordinate multiply that by your scale and abra cadabra you have a chart. takes some practice but youll get it. nick

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nick545423y ago
I'm sure his intentions are good but its too many calculations for something extremely simple. YMin is the bottom of the grid and YMax is the top. a is the actual width in pixels of each grid and YScale is the yaxis width YScale: dont even bother with YScale its not used b is the actual distance to offset the y lines so then he just iterates through the points on the chart grid and plots them out according to its coordinates and draws a line I made one in jave for a 2d applet that auto scales and sizes based on tons of different variations and if you hacked at the code, organized it and gave meaningful names you could triple its effeciency. If you could come of with an algorithm to use bit shifting as opposed to multiplication you could handle larger loads. Multiplying is so over bearing on a cpu. its easy though you have a client grid area rectangle. thats your x and y. determine where the grid axis is based on use those variables to calculate based on a 0 base axis. then when you have the coordinate multiply that by your scale and abra cadabra you have a chart. takes some practice but youll get it. nick