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art-ganseforth
04-02-2016, 06:18 AM
Hi there,

my project is described here:
https://www.opengl.org/discussion_boards/showthread.php/198350-Render-offscreen-to-texture-basic-questions?goto=newpost

... and it is still flickering.

There are two modules (classes) sharing most of their functions, as there are especially the creation and destroying-function, the pointer-management, etc. Both functions are performing two render-passes. The first pass generates a texture for later use, while the second one generates a preview-thumbnail as output in the modules-window.
Inside, one module is rendering two 2d-textures for blending them (works), while the other one renders some single-colored quads (causes flickering of the main-output).

Here is the code (i know, that some things i do, can be done more elegant, but this i'll do later...)

Working code (note: for each module, GLbuffer is the class containig the associated output-texture - the code for GLBuffer.Set(w,h) you'll find below):


w = vcW->GetValue(); h = vcH->GetValue();

if (w != GLBuffer.W || h != GLBuffer.H) GLBuffer.Set(w,h);

GLuint FBO;
glGenFramebuffers(1, &FBO);
glBindFramebuffer(GL_FRAMEBUFFER, FBO);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, GLBuffer.Texture, 0);


glViewport (0, 0, (GLint)w, (GLint)h);

glClearColor (0.0, 0.0, 0.0, 1.0);
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glMatrixMode (GL_PROJECTION); glLoadIdentity(); gluPerspective (90.0, 1, 0.9, 3);
glMatrixMode (GL_MODELVIEW); glLoadIdentity(); glTranslatef (0, 0, -1);


glEnable (GL_TEXTURE_2D); glDisable(GL_BLEND);

if (src1 > 0) {
double sc = vcScale1->GetValue();
double r = vcRotate1->GetValue();
double x = vcX1->Get01();
double y = vcY1->Get01();

glBindTexture (GL_TEXTURE_2D, _TEXTURE(src1));
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);

glPushMatrix();
glRotatef (r, 0.0, 0.0, -1.0);



glBegin(GL_QUADS);
glTexCoord2f (x , y ); glVertex3f (-sc, sc, 0);
glTexCoord2f (x+1, y ); glVertex3f ( sc, sc, 0);
glTexCoord2f (x+1, y+1); glVertex3f ( sc, -sc, 0);
glTexCoord2f (x , y+1); glVertex3f (-sc, -sc, 0);
glEnd();
glPopMatrix();
glFlush();
}

int blendSrc = blendSrcVal[selBlend1->GetValue()]; int blendDst = blendDstVal[selBlend2->GetValue()];
glEnable (GL_BLEND);
glBlendFunc (blendSrc, blendDst);

if (src2 > 0) {
double sc = vcScale2->GetValue();
double r = vcRotate2->GetValue();
double x = vcX2->Get01();
double y = vcY2->Get01();

glBindTexture (GL_TEXTURE_2D, _TEXTURE(src2));
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, tmodeVal[selTexMode->GetValue()]);

glPushMatrix();
glRotatef (r, 0.0, 0.0, -1.0);

glBegin(GL_QUADS);
glTexCoord2f (x , y ); glVertex3f (-sc, sc, 0);
glTexCoord2f (x+1, y ); glVertex3f ( sc, sc, 0);
glTexCoord2f (x+1, y+1); glVertex3f ( sc, -sc, 0);
glTexCoord2f (x , y+1); glVertex3f (-sc, -sc, 0);
glEnd();
glPopMatrix();
glFlush();
}

glBindFramebuffer(GL_FRAMEBUFFER, 0);
glActiveTexture(GL_TEXTURE0);
glDeleteFramebuffers(1, &FBO);

Canvas->Refresh();


Flickering:


w = vcW->GetValue(); h = vcH->GetValue();

if (w != GLBuffer.W || h != GLBuffer.H) GLBuffer.Set(w,h);

GLuint FBO;
glGenFramebuffers(1, &FBO);
glBindFramebuffer(GL_FRAMEBUFFER, FBO);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, GLBuffer.Texture, 0);


glViewport (0, 0, (GLint)w, (GLint)h);

glClearColor (0.0, 0.0, 0.0, 1.0);
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glMatrixMode (GL_PROJECTION); glLoadIdentity(); gluPerspective (90.0, 1, 0.9, 3);
glMatrixMode (GL_MODELVIEW); glLoadIdentity(); glTranslatef (0, 0, -1);


glDisable (GL_TEXTURE_2D); glDisable(GL_BLEND);

for (double cx = 0; cx < w; cx = cx++) {
for (double cy = 0; cy < h; cy = cy++) {
double tr=0,tg=0,tb=0,ta=1;
double pxs = cx * 2 - w;
double pys = cy * 2 - h;
double px = fabs((pxs+1) / w); double lxf = (sin(px * LiW)/2+0.5);
double py = fabs((pys+1) / h); double lyf = (sin(py * LiH)/2+0.5);
double rr = px + py;
double rc = pow(px * px + py * py, 0.5);
double rs = px > py ? px : py;
double rad = shape < 0 ? ((1 + shape) * rc - shape * rr) : ((1 - shape) * rc + shape * rs);
rad = (rad * inner - inner + 1) / 2;
rad = rad > 1 ? 1 : rad < -1 ? -1 : rad;
double dif = pow(cos(rad * M_PI), 1 / edge) + (1-lxf*lyf)*LiF;
if (dif >= 0) {
double nze = 1.0 - (noise == 0 ? 0 : fmodf(rand(), noise) / 256);
tr = (dif * r) * nze;
tg = (dif * g) * nze;
tb = (dif * b) * nze;
tr = (tr > 255 ? 255 : tr)/255;
tg = (tg > 255 ? 255 : tg)/255;
tb = (tb > 255 ? 255 : tb)/255;
}
else {
tr = 0;
tg = 0;
tb = 0;
ta = 1;
}
glBegin(GL_QUADS);
glColor4f(tr, tg, tb, ta); glVertex3f ((pxs-0)/w, (pys-0)/h, 0);
glColor4f(tr, tg, tb, ta); glVertex3f ((pxs+2)/w, (pys-0)/h, 0);
glColor4f(tr, tg, tb, ta); glVertex3f ((pxs+2)/w, (pys+2)/h, 0);
glColor4f(tr, tg, tb, ta); glVertex3f ((pxs-0)/w, (pys+2)/h, 0);
glEnd();
}
}
glFlush();

glBindFramebuffer(GL_FRAMEBUFFER, 0);
glActiveTexture(GL_TEXTURE0);
glDeleteFramebuffers(1, &FBO);

Canvas->Refresh();


The following functions are part of GLbuffer-class and used by both (note: "Texture" is a gl texture pointer created with the module):


clsBuffer *clsBuffer::Set(int w, int h, wxString name, int depth) {
if (name != "") Name = name;
useAlpha = true;
TexEmpty(w,h);
return this;
}

clsBuffer *clsBuffer::TexEmpty(int w, int h, bool ua) {
W = w; H = h;

glBindTexture (GL_TEXTURE_2D, Texture);
glTexImage2D (GL_TEXTURE_2D, 0, GL_RGBA, W, H, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);

glTexEnvf (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

return this;
}




What i already found out is:
- The thumbnail for both modules is generated correctly. So the renderin-process itself works fine.
- Flickering appears each time, the module is updated, which may be n times slower then the main-output.
- If the update-frequence is identical to the main output (n=1) the main output stays totally black.
- The module-thumbnail doesn't flicker. Only the main-output and some other preview-windows.
- Commenting out the GLBuffer.Set(w,h)-call which is only needed for resizing, has no effect on the problem.
- Most strange: Commenting out the four lines between glBegin(GL_QUADS); and glEnd();, flickering stops.


Any ideas what is wrong???

Maybe i'm blind and i do not see some very simple thing...



Thanks for reading,

Frank

art-ganseforth
04-03-2016, 05:56 AM
calling

glColor4f(1, 1, 1, 1);
after drawing stops the flickering. Obviuosly the color-setting takes influence on further renderings - even when they use textures only.

Agent D
04-04-2016, 12:25 AM
Yes, in the fixed function pipeline, the color set with glColor* stays the same until it is changed
and all further vertices use that color.

When your geometry is textured, the texture color is combined with the interpolated vertex color
that you set via glColor* (typically multiplied, can be set via texture environment).