[Piglit] [PATCH 2/2] drawpix-z: test glDrawPixels(GL_DEPTH_COMPONENT)

[Brian Paul]

On 06/11/2012 10:16 AM, Eric Anholt wrote:
> On Fri,  8 Jun 2012 14:31:16 -0600, Brian Paul<brianp at vmware.com>  wrote:
>> diff --git a/tests/general/drawpix-z.c b/tests/general/drawpix-z.c
>> new file mode 100644
>> index 0000000..cdd6ac9
>> --- /dev/null
>> +++ b/tests/general/drawpix-z.c
>
> The code would have made more sense to me if you had:
>
> float ndc(float z)
> {
>          return -1.0 + 2.0 * z;
> }
>
>> +static void
>> +draw_z_gradient(GLfloat zLeft, GLfloat zRight)
>> +{
>> +	GLfloat verts[4][3];
>> +
>> +	verts[0][0] = -1.0;  verts[0][1] = -1.0;  verts[0][2] = zLeft;
>> +	verts[1][0] =  1.0;  verts[1][1] = -1.0;  verts[1][2] = zRight;
>> +	verts[2][0] =  1.0;  verts[2][1] =  1.0;  verts[2][2] = zRight;
>> +	verts[3][0] = -1.0;  verts[3][1] =  1.0;  verts[3][2] = zLeft;
>
> 	verts[0][0] = -1.0;  verts[0][1] = -1.0;  verts[0][2] = ndc(zLeft);
> 	verts[1][0] =  1.0;  verts[1][1] = -1.0;  verts[1][2] = ndc(zRight);
> 	verts[2][0] =  1.0;  verts[2][1] =  1.0;  verts[2][2] = ndc(zRight);
> 	verts[3][0] = -1.0;  verts[3][1] =  1.0;  verts[3][2] = ndc(zLeft);
>
>> +enum piglit_result
>> +piglit_display(void)
>> +{
>
>           float left = epsilon;
>           float right = 1.0 - epsilon;
>
>> +
>> +	/* create image of Z values increasing from left to right */
>> +	buf = (GLfloat *)
>> +		malloc(piglit_width * piglit_height * sizeof(GLfloat));
>> +	for (j = 0; j<  piglit_height; j++) {
>> +		for (i = 0; i<  piglit_width; i++) {
>> +			float z = i / (float) (piglit_width - 1);
>> +			z = epsilon + (z * (1.0 - 2.0 * epsilon));
>
>                          z = left + i * (right - left);
>
>> +			buf[j * piglit_width + i] = z;
>> +		}
>> +	}
>> +
>> +	/* draw a red quad behind the Z gradient - it should not be visible */
>> +	glColor4fv(red);
>> +	draw_z_gradient(-1.0 + 2.0 * epsilon, 1.0);
>
>          draw_z_gradient(left + epsilon, right + epsilon);
>
>> +	draw_z_gradient(-1.0, 1.0 - 2.0 * epsilon);
>
>          draw_z_gradient(left - epsilon, right - epsilon);
>
> With the code you had, if I'm reading this right, the epsilon in
> drawpixels is on a different scale from the epsilon in draw_z_gradient,
> so on the +/- (1.0 - 2.0 * epsilon) side, the zs are equal to the
> z that was DrawPixels()ed, and basically you're getting lucky.

Since the Z ortho range was [-1,1] while zbuffer vals are [0,1] I was 
off by a factor of two.  My epsilon was large enough to hide that. 
BTW, having a tight epsilon isn't a concern in this particular test.

Thanks for the review.  I think I can simplify this further by simply 
using an ortho projection such that Z is in [0,1] instead of [-1,1]...

-Brian