GL11.glEnable(GL11.GL_STENCIL_TEST);

GlStateManager.colorMask(false, false, false, false);
GlStateManager.depthMask(false);

GL11.glStencilMask(0xFF);
GL11.glClearStencil(0);
GL11.glStencilFunc(GL11.GL_NEVER, 1, 0xFF);
GL11.glStencilOp(GL11.GL_REPLACE, GL11.GL_KEEP, GL11.GL_KEEP);

GL11.glStencilMask(0xFF);
GL11.glClear(GL11.GL_STENCIL_BUFFER_BIT);
this.drawTexturedModalRect(i, j, 0, 0, this.xSize, this.ySize);

GlStateManager.colorMask(true, true, true, true);
GlStateManager.depthMask(true);
GL11.glStencilMask(0x00);

GL11.glStencilFunc(GL11.GL_EQUAL, 1, 0xFF);

this.drawTexturedModalRect(i + 25, j, 0, 0, this.xSize, this.ySize);

GL11.glDisable(GL11.GL_STENCIL_TEST);