Present of uninitialized color attachment issue

Question

When I run my OpenGL app, I get the following error:

I googled but can't get any useful information.

Here're a piece of source code:

- (void)render:(CADisplayLink*)displayLink {
    [self.canvas clear];
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
    glEnable(GL_BLEND);

    NSInteger mLength = mParticles.count;
    NSInteger drawCount = 0;
    NSInteger drawIndex = 0;
    WQParticle* drawParticle;
    CGFloat drawX,drawY,drawScale,drawAngle;
    GLKMatrix4 changeColorMatrix;
    if (mLength > 0){
        glBindFramebuffer(GL_FRAMEBUFFER, FBO);
        glViewport(0,0,width,height);
        drawCount = 0;
        drawIndex = -1;
        while ( drawCount < mLength){
            drawParticle = mParticles[drawCount];

            if(!(drawParticle.flg && random > 0.5)){

                if (drawIndex != drawParticle.texIndex) {
                    glActiveTexture(GL_TEXTURE0);
                    glBindTexture(GL_TEXTURE_2D, (GLuint)(texture[drawParticle.texIndex]));
                    glUniform1i((GLint)uniLocation[1], 0);
                    drawIndex = drawParticle.texIndex;
                }

                if(drawParticle.flg){
                    drawX = drawParticle.posX + (random * 1 - 0.5) * drawParticle.scale * 0.06;
                    drawY = drawParticle.posY + (random * 1 - 0.5) * drawParticle.scale * 0.06;
                    drawScale = drawParticle.scale * (random * 0.4 + 0.8);
                    changeColorMatrix = [self setChangeColorWithDp:drawParticle n:random];
                    drawX = drawX / drawScale;
                    drawY = drawY / drawScale;
                }else{
                    drawX = drawParticle.posX / drawParticle.scale;
                    drawY = drawParticle.posY / drawParticle.scale;
                    drawScale = drawParticle.scale;
                    changeColorMatrix = [self setChangeColorWithDp:drawParticle n:1];
                }
                glUniformMatrix4fv((GLint)uniLocation[2], 1, 0, changeColorMatrix.m);
                drawAngle = drawParticle.angle;
                CGFloat drawR = sqrt(drawX * drawX + drawY * drawY);
                CGFloat oa = 2 * M_PI - acos(drawX / drawR);
                drawX = cos(oa - drawAngle) * drawR;
                drawY = sin(oa - drawAngle) * drawR;

                mMatrix = GLKMatrix4Identity;
                mMatrix = GLKMatrix4Rotate(mMatrix, drawAngle, 0, 0, 1);
                mMatrix = GLKMatrix4Scale(mMatrix, drawScale, drawScale, drawScale);
                mMatrix = GLKMatrix4Translate(mMatrix, drawX, drawY, 0);
                mvpMatrix = GLKMatrix4Multiply(f_tmpMatrix, mMatrix);

                glUniform1i((GLint)uniLocation[3], YES);
                glUniformMatrix4fv((GLint)uniLocation[0], 1, 0, mvpMatrix.m);
                glDrawElements(GL_TRIANGLES, sizeof(indices), GL_UNSIGNED_BYTE, 0);
            }

            if (drawParticle.life > 0) {
                [mVF getForceFromPosWithPx:drawParticle.posX Py:drawParticle.posY];
                [drawParticle setVFupdateWithOutX:mVF.outX OutY:mVF.outY];
                drawCount++;
                continue;
            }
            [mParticles removeObjectAtIndex:drawCount];
            mLength = mLength - 1;
        }
        glBindFramebuffer(GL_FRAMEBUFFER,0);
    }

    glBindTexture(GL_TEXTURE_2D, FBOTexture);
    mMatrix = GLKMatrix4Identity;
    mvpMatrix = GLKMatrix4Multiply(tmpMatrix, mMatrix);
    glUniformMatrix4fv((GLint)uniLocation[0], 1, 0, mvpMatrix.m);
    glUniform1i((GLint)uniLocation[3], NO);
    glDrawElements(GL_TRIANGLES, sizeof(indices), GL_UNSIGNED_BYTE, 0);
    [self.canvas.glContext presentRenderbuffer:GL_RENDERBUFFER];
}

How can I solve this?

Answer 1

Check that glViewport() is set the size of the renderpass you are rendering to, and that either glScissor() is set to that size too, or that scissor test is disabled via glDisable().