Thread: How to implement such a scroll bar?

The way I write scrollable windows is to call GetTextMetrics in the WM_CREATE routine to get the character width and height that is based on the systems font which normally does not change during a Windows session. Also, I track the size of the client area in the WM_SIZE routine where LOWORD(lParam) is the X value and HIWORD(lParam) is the Y value. This is basis for aligning text using TextOut to display the data in the client area.

If possible, how about posting some of your code so that we can see what you have so far.

Someone guided me to using GetTextExtentPoint32, which computes the width and height of a string of text. so now, I know the width of the whole content, and the number of lines would be "widthOfString / widthOfClientArea", but now how do I draw each line?

See the well-known sample from Petzold which does exatly that, posted many times on usenet..

The code is rather simple, it reads a text file and displays the text, now the difficulty comes to the "scrolling", how do I know the number of lines?

Can you upload a representative sample of the text file? Thus, possible solutions can be tested prior to posting those solutions.

Originally Posted by Alex31

See the well-known sample from Petzold which does exatly that, posted many times on usenet..

I was reading the book by Petzold, and there was indeed an example showing how to create scroll bars and how to scroll text. but the text he was using was not read from a text file, it was just an array whose number of lines was known before he run the program, and he didn't deal with word break cause the program he was demonstrating was displaying something like a table, or a spread sheet.

Originally Posted by kevintse

I was reading the book by Petzold, and there was indeed an example showing how to create scroll bars and how to scroll text. but the text he was using was not read from a text file, it was just an array whose number of lines was known before he run the program, and he didn't deal with word break cause the program he was demonstrating was displaying something like a table, or a spread sheet.

You can use the Sysmets3 example with a dynamic struct array instead of the static struct that he is using in the example. For instance, the following code can be used with the example. This code reads in all the lines from an ASCII text file. You would do all your preliminary processing such as word breaks etc. when loading the file into the struct array. I've already implemented the following in sysmets3 to verify that it works.

Code:

#include <stdio.h>
#include <string.h>
#include <windows.h>
#include <stdlib.h> 

struct node {
	TCHAR * szSentence ;
};

struct node **sysmetrics = NULL;
ULONG NUMLINES = 0;

void AddSentenceToStruct( char *pSentence)
{
	sysmetrics = (struct node **)realloc(sysmetrics, (NUMLINES + 1) * sizeof(struct node *));
	sysmetrics[NUMLINES] = (struct node *)malloc(sizeof(struct node));
	sysmetrics[NUMLINES]->szSentence = strdup(pSentence);
	NUMLINES++;
}

int main(int argc, char **argv)
{
	int iIndex = 0; 
	FILE *hFile;
	char szBuffer[MAX_PATH+1];

	hFile = fopen ( argv[1], "rb" );
	if ( hFile == NULL ) {
		printf("Unable to open the file\n");
		return -1;
	}
	while( fgets(szBuffer, MAX_PATH, hFile) != NULL)
	{
		fgets(szBuffer,MAX_PATH,hFile);
		AddSentenceToStruct(szBuffer);
	}
	fclose (hFile);
	for(iIndex = 0; iIndex < NUMLINES; iIndex++) {
		printf("[%d]->str: %s", iIndex, sysmetrics[iIndex]->szSentence);
	}
	/* free all sysmetrics elements */
	for(iIndex = 0; iIndex < NUMLINES; iIndex++) {
		free(sysmetrics[iIndex]->szSentence);
		free(sysmetrics[iIndex]);
	}
	free(sysmetrics);
	return 0;
}

This approach just fixes my problem, all I need is dynamic memory allocation.
Now I can compute how many characters will fit one line, and I can put the character string for each line in the struct...
Thank you, Bob, Thank you for your time.