Trouble with OpenGL and blending

[Johanovski]

Hi there!

I'm working with a 3D OpenGL application and I'm having a problem with blending functions. In my scene there are some solid objects that are drawn each frame. When the player touches the screen I want to show a kind of "flash" in the screen, and I've thought I can do this by showing a white square in front of everything and then reducing it's alpha until it's gone. The effect seems to work, but the problem is that when the withe layer is transparent no others objects are shown (so solid objects disappear since the white layer has completely disappeared, and then objects are drawn again. I'm quite new to OpenGL so I don't understand how exactly it works, can anyone take a look at my code and tell me what I'm missing?

// Initializing OpenGL
const GLfloat zNear = 0.1, zFar = 1000.0, fieldOfView = 60.0;
    GLfloat size;
	
	glEnable (GL_BLEND);
	glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
	glShadeModel (GL_FLAT);
	
    glEnable(GL_DEPTH_TEST);
    glMatrixMode(GL_PROJECTION);
    size = zNear * tanf(DEGREES_TO_RADIANS(fieldOfView) / 2.0);

    CGRect rect = self.bounds;
    glFrustumf(-size, size, -size / (rect.size.width / rect.size.height), size / (rect.size.width / rect.size.height), zNear, zFar);
    glViewport(0, 0, rect.size.width, rect.size.height);
	
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

(...)

// Main drawing loop
[EAGLContext setCurrentContext:context];    
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
    glViewport(0, 0, backingWidth, backingHeight);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glMatrixMode(GL_MODELVIEW);
    
    glTexCoordPointer(2, GL_SHORT, 0, squareTextureCoords);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

if (showFlash) {
		[self showFlash];
	}

(...) <-- Other solid alpha-less objects are drawn here

glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];

(...)

// showFlash function
const GLfloat vertexs[] = {
		
		// Define the layer
		-1.0, 1.5, -1.0,             // top left
		-1.0, -1.5, -1.0,           // bottom left
		1.0, -1.5, -1.0,            // bottom right
		1.0, 1.5, -1.0				// top right
	};
	
	glPushMatrix();
    {		
		glVertexPointer(3, GL_FLOAT, 0, vertexs);	
        glEnableClientState(GL_VERTEX_ARRAY);

		glColor4f(1.0f, 1.0f, 1.0f, flashAlpha);

        glBindTexture(GL_TEXTURE_2D, textures[6]); // <-- It's a white image!
		glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
		
		flashAlpha -= 0.05;
		if (flashAlpha <= 0) {
			showFlash = FALSE;
		}

		glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
    }
    glPopMatrix();

Any clue about this...? Thanks in advance!

[Johanovski]

Solved! ^_^

Don't know why, but just drawing the white layer after the effects get it working (in fact it have sense... I think I've spent too many hours with OpenGL and I'm starting to feel unable to solve a 2+2 operation U_U')!